You are a 15 year old boy. Fasting is probably not a good idea unless you're willing to risk not reaching your full height. Seriously, fasting is a great way to lose fat, but not when your body is still growing and wanting ridiculous amounts of food (I've seen teenage boys eat, it's madness). I don't know whether or not you are overweight or just wanting to be healthier, but there are much better ways of going at it at your age. Really, just enjoy life and don't obsess so much over food right now. Your teen years are supposed to be fun.
F 28/5'4/100 lbs
"I'm not a psychopath, I'm a high-functioning sociopath; do your research."