We were all 15 once and I'm sure for a lot of us it wasn't the best of times. I will admit to going slightly in the opposite direction to the path my parents wanted for me albeit temporarily but I was rude, self centred, dramatic and a downright little bitch for a time.
I'm not proud to say that I broke my mum's heart on a fair few occasions, why? Because I was 15, trying to find my place in the world and I didn't think anyone could ever understand how hard my life was (My life was in no way hard).
I came through it though, settled down, got my exams and I have a really close relationship with my mum.
I didn't like those early years of being a teenager, I think it was all just too much at once - Hormones, exams, boys, friends, social expectations, the potential list of perceived problems really is endless when you're 15.
It's normal to feel frustrated with your daughter OP, just persevere, continue loving and believing in her, she will hopefully come out the other side.
Good Luck!