@allthegoodusernameshavegone
Well it was a loooong time ago,I’m 49, but many a time mine or my friends parents would take a holiday for a week and we 14 /15 year olds would move in to keep said left teen company then during the school holidays we would all as a group go on camping holidays, usually by train or hire a mini bus from a taxi firm or generous Dad for a week with no parents present without issue. But our parents (now in their 70s) were of the generation that left school and went into apprenticeships at 14/15 so didn’t look upon us as so vulnerable, I don’t understand why we don’t put more trust and responsibility in our teens instead of hindering their natural development to grow up.
I'm even older than you, and we were far more 'free range' than children are now - but there is no way on Earth that my parents would have gone away and left us unsupervised at that age, and no way any of my friends' parents would have done, either. There were a few 'cool' girls whose parents occasionally left them unsupervised for a weekend, which would invariably end in tales of people vomiting, crying and having sex while trashing the absent parents' house. One of the particular offenders was a 'nice girl', or so her parents thought.
I was genuinely a very, very boring teenager who did nothing at all. Knowing what sorts of things teenagers get up to, though, suggest to me that even if you honestly think you can vouch for your own child, you absolutely can never vouch for their friends.
I say this after many, many long years of raising children to adulthood and almost-adulthood. And you wouldn't believe the number of times that the DC have said to me over the years (about such gatherings) variously: "But what could possibly go wrong?"; "But you like X, and it's at her house"; "but his mum will lock up the drinks" (which, obviously, means nobody will ever bring anything in); "OMG, you are so LAME, you're the ONLY parent who's like this" (when I know that's not true). Oh, and "You never give me ANY freedom" (this from a DC who was frequenting nightclubs with fake ID at 15). And so on...