Hmm this is interesting, I'm only 20 so 15 was not very long ago for me... But I would say
Enjoy high school and don't rush through it
Don't worry about girls, you won't end up with any of the ones you know now
Stay away from girls named anna.
Do every club, sport, activity you can and work harder
Just be yourself, you won't remember any of the people from High school anyways so don't worry about trying to please them
Learn jiu jitsu
Put God first in everything and always do what is right no matter how bad it hurts you.
And ALWAYS listen to your parents, you don't know better than them.