You really havent given enough detail. What training are you doing? what goals do you have?

At 15 years old, the best thing to do is to cut out processed and convenience foods, limit the amount of soda's and puddings you indulge in, and eat good home cooked meals, with plenty of veg and fruit.

If you eat natural foods, and keep yourself active, then your body will sort itself out. You are still very young, so as it stands, you should not be in such a hurry, and also, your body will go through huge changes over the next 3-5 years as you reach full maturity, so now is not the time to deprive or starve it.
Don't let the door hit ya' where the good lord split ya'