Pretty much all good advice above. A couple things:
1) You're 15, you aren't going to get all that strong, yet. I left HS at 6'2" and 148lbs. I've since gained about 40lbs of muscle.
2) Your Press is actually you best lift relatively.
3) Deload only when you've missed a lift more than twice, and then only 10%. So if you miss a rep or two on squats, just go back next time and do the same lift. If you miss it again, then maybe deload 10%.
4) Micro weights, get some chain and a carbiner (google for directions)
I couldn't get bigger than about 150 lbs until I was 22, don't sweat it too much.
"Go For Broke"
Fat Kine-230/24% @ 6'2"