15 mbps should be plenty for a HD stream, although probably not for 4K. If you’re watching HD content, I’d say either your network speed is highly variable, or you have interference from other wifi signals, or you have other activity on your network. Is the TV the only active connected device when you see rebuffering? Are you connected via wifi? 2.4 GHz or 5 GHz? You might want to check a wifi analyzer and see if there are other networks visible on your channel, and try switching channels. If your router is far from your TV you should use 2.4 rather than 5 GHz because 2.4 has better range. And although 2.4 GHz has 11 channels, the only ones you should use are 1, 6 or 11.
What is the basis of this rather dubious advice? My general rule is that if you’re going to manually select a channel, the one to use is the one that no one else is using within detectable range.
Back on topic, my answer to the poll was “never”, but based only on Netflix. It’s kind of surprising as my wireless connection to the router is through an old Linksys WRT-54G acting as a bridge (via Tomato firmware) located one floor down and on the opposite side of the house from where the router is. But because the bridge has dual external antennas its sensitivity is pretty good. I think Netflix uses some clever technology to deliver a smooth streaming experience even with limited bandwidth. I’ve not much experience with other services.
My actual wired Internet service should be more than adequate. I signed up for what was supposed to be 150 Mbps service but they’ve been gradually ramping it up under the same plan. I remember seeing it at 300 Mbps, and I just ran a speed test now and it’s over 400. Not that I’m complaining. But the bastards can afford it. I just checked my bill to confirm what service level I’m actually paying for, and yes it’s theoretically the 150 tier, but rates have gone up A LOT since the last time I paid attention!
And as @markn_1 noted, 15 Mbps or even less over wireless should be more than sufficient for reliable streaming, even for 1080p. Probably not quite good enough for 4K, though, but I don’t bother with that.
I haven’t noticed any buffering problems with Amazon or Netflix. Sometimes the wireless connection from our router downstairs to the Xbox on the main floor is a bit flaky, but that generally results in no connection, not a poor connection.
I have noticed Youtube downgrading video quality drastically from time to time and my wife has complained about occasional buffering when streaming movies from the library via Kanopy (both on a wired connection).
Mine never buffers, but it does fail completely on occasion. Other times a streaming service will bug out; I just go watch another service.
I know mine have buffered in the past but I honestly can’t remember when. But then, most of my watching is at other than prime time because of my work schedule.
To make a minor correction, when I select a show, there’s a 2-3 second buffer on most apps. But very, very few once started.
I can’t say it never ever happens but never was the best answer. On any given evening it generally never happens. But sometimes with network issues it can. This is on 2 connections (vacation home and regular) the slowest is 25mb/s, the other at 300 mb/s .
I don’t stream that much because I still have Uverse, but I do stream Netflix, Amazon Prime, and HBO Max. I’ve never had a single problem with buffering.
1, 6 and 11 don’t overlap each other. The intermediate channels overlap. So if your neighbor is using 6 and you select 3 because “no one is using it”, you’ll still get interference from channel 6. Most auto selection software will select 1, 6 or 11. So staying on those three channels protects better against new networks appearing later. Here are some cites:
I watch Amazon Prime, Netflix, and YouTube without any buffering necessary.
As others have said, I get more buffering with HBO than Netflix or Prime.
On the other hand, we stream Netflix and Prime through apps on our DVD player. For HBO Max, I use a Chromecast and stream from my phone to the TV. Don’t know if that has anything to do with it or not. It’s still all WiFi, one way or the other.
On the other other hand, Prime does this weird thing where about the first 30-60 seconds of any program is very low-res until it clears up and it is fine for the rest of the episode, then at the beginning of the next episode it does it again.
That’s due to adaptive streaming. At the beginning of the stream, it doesn’t yet know what your network speed is, so it picks a low resolution stream to be safe. When it has enough data to know that your network can support it, it upshifts to a higher-resolution stream. There are ways to avoid this, like remembering your speed from the last stream, but it’s more risky because your effective network bandwidth may have changed since then.
I typically get no buffering, 200 megabit Comcast Business connection.
Back on 3 MB DSL I got a lot of buffering, especially at the beginning of shows or if anyone else in the house was doing anything bandwidth-intensive.
I selected never, though in truth it may happen once every few months if we have internet issues. We mainly watch Netflix and Disney +. The devices (TV, Xbox X, PS4) are all wired to the modem/router, and download speed is consistently 90 - 100 mbs.
For those that are selecting never, is changing the channel instantaneous like with an analog/cable/satellite signal?
Maybe once every month or so, it’s rare. I checked Never since even 1 daily (the minimum choice for the other options) is dramatically more often than I experience. I was an early adopter to various streaming services, back in the late 2000s I certainly remember streaming video usually buffering multiple times a day, but in the last 5-6 years, it’s become very rare.
As for changing the channel, I usually navigate between content within a streaming service or occasionally will switch from say, Netflix to Amazon Prime. I’m not normally “changing channels” (I don’t usually carry a over the top cable package with traditional channels.)
Well, with Netflix there aren’t “channels” but yes it buffers when I start watching something. I didn’t think this was what the OP was getting at though? I was picturing buffering that interrupts the program partway through.
I’ve got a 100mbps VDSL connection from AT&T (“Internet 100”) and we just about never actually run into buffering in normal circumstances. This is usually streaming full HD video and someone doing something else on the PC in the other room - video gaming, watching YouTube, streaming something else, and so on.
Every now and again, the ISP will have some sort of issue/slowdown and we may end up with buffering at that point, but that’s pretty rare.
Mostly, if not always, on YouTubeTV, especially our local channels. Quite annoying when watching the news, or even worse - Jeopardy! 
I picked 6-10, tho sometimes it hardly happens at all, but other times…
I said 1 - 5 times but I wasn’t sure what the time period was. Ever? Most of our streaming almost never buffers but we have fast internet and a repeater from the modem to our TV. Before we had that Netlfix often buffered.