This is unbelievable. I did more than this when I was 8, never mind 15!
Given you must have been 15 at some stage, I'm surprised you have to ask.
At 15 they need to be essentially totally independent. Not to the extent that they do everything for themselves, but they need the ability to do so.
They need to know how to make their own meals, do their own washing and ironing, be able to look after siblings or pets, make drinks, get up by themselves, get dressed, do their own homework, go to bed. They should also know how to clean any room in the house and ideally do so without having to be asked a few times a week.
It's not outrageous that a sensible 15 year old could be left home alone for a night. At 16 or 17 I'd be surprised if they haven't.
I really hope this ship hasn't sailed, because I don't see how any one could claw their way to holding down any responsibility if they haven't been conditioned with the basics. I feel for whoever has to live with her in the future.
If she can't do this how do you expect her to cope with any sort of job when she turns 16?
And packing the school bag is completely nuts!! They're entitled to privacy at that age and I would have gone off it if my parents went through my bags for no reason at that age. That's incredibly violating and in all honesty, it sounds like you and her father haven't treated her properly at all.