Originally Posted by J_R_B
At 15, concern yourself with a proper healthy diet and exercise. Don't try to lose weight while you are still growing (unless you are obese and a doctor tells you to, which doesn't seem like the case with you).
I was 99kg earlier this year, but am still considering going down because I still have a fare bit of fat surrounding the abdominal area and chest, so weight loss and light weight training will help. I am also hoping that this weight loss will help me with my knee more than it has already.