Lyric question: fifteen-stone first-footer?

The term ‘fifteen-stone first-footer’ is used in the Marillion tune ‘Uninvited Guest’. I assume, through context, that it’s something you really don’t want to deal with, and I figure it’s a term from Great Britain, but I’m at a loss as to what the term actually means. Anyone able to enlighten?

Fifteen stone relates to weight. In the UK 14 pounds is equal to one stone.

First-footer is a scottish thing. At New Year (also called Hogmanay) the first person to visit after midnight (the Bells) is the first foot. Traditionall it’s supposedf to be a dark-haired man carrying a lump of coal, but it’s usually just a friend or neighbour carrying a massive amount of booze.