I know your trying to be approximate, but 20C is 68F. comfortable if your working, but I’m an office worker. 68F is on the cold side for sitting at a desk or watching TV… And 15C? That may be a pleasant cool day where you come from, but when you get abit older you’ll call that “cold”
140F (60C) is that maximum acceptable surface temperatue by the standard we use at work. At 60C you can touch typical metal parts, and get your hand away quick enough to not get burned (unless you are old or a child), It’s also about as hot as you can hold without doing real damage, but it’s not a temperature you can use for things you want people to hold, because they will get burned.
You can sit on a wooden surface in 100 C sauna and while it may feel uncomfortably hot for a moment before the surface cools down it won’t burn you. If you have any metal jewelry on you it’ll be ok as long as it is constantly in contact with your skin. But if your cross or dogtags hangs freely in the air and then you lean back and let it touch your skin after it has had time to heat up it will burn you.
I run warm. I routinely roll my sleeves up in our office, sometimes while sitting next to a woman who is shivering under a shawl. I probably should have mentioned that. Those descriptions work for me. They might not work for people who run cooler.