You're 15 years old, you really shouldn't be taking anything except food. If you really want to cut up just be careful with what you eat. Considering the fact that you aren't old enough to lift in many gyms you shouldn't even think about supplementing; you are faaaar from any plateau.
Etomic has the right idea here. Even irregardless of age, supplements are two sided: either you can make
effective and reasonable use of them when combining with a good diet, or you can fritter away countless dollars without the proper diet. In my few years of helping people I've seen plenty of the first, but far more of the latter. This stuff can really add up when people start adding product after product and just getting... nowhere.
I'll leave it at this. I think you are going to get
far more results as a better solution:
1. Work out a diet, with the aid of a nutrition subforum. It doesn't have to be perfect counting number of peas (I've had someone ask), but you should have a good, clear picture of your macros (P/C/F) and total intake.
2. If you don't have a constructed training program, I suggest following one of the premade ones that are popular (rippetoe, max-OT, 5x5, etc). If you do, awesome.
3. Start with basic supplements. Yes, the basics go a long way - to this day, I still prefer V12 Turbo (our relatively simple product) over complex formulas. With parental/guardian consent, I suggest:
a. Multivitamin
b. Fish oil
c. Creatine monohydrate
optional, and definitely w/ consent!
It's a simple starting point, but it gives you a solid platform to go from. Too many people skimp on 1 and 2 (and I originally did) and jump too far into supplementation.