I'm 15 and my hair is thinning (Photo)

Maybe you have juvenile hair loss.  Maybe you have hair loss that is not genetic. Maybe you have an autoimmune disease. Maybe you have too much stress. Maybe it is telogen effluvium.The Internet will leave you with lots of maybes.An examination by a doctor may give you a diagnosis.When you have a diagnosis you can explore treatment options.

I my opinion you should be evaluated for hair loss by a dermatologist  or hair specialist.They will usually  perform  a thorough exam, history, blood work and possibly biopsy. There are many good options available once the diagnosis  is obtained.Good luck!

Unfortunately some guys do show signs of male pattern balding from an early age. This might not be the case for you and you might just have a naturally thin hairline that doesn't deteriorate at all. I suggest you take some good quality photos and compare the appearance of your hairline in 6 and 12 months. A positive history of early receding hairlines on your mother or father's side of the family might be a bad prognostic indicator. 

Men frequently go from a juvenile to a mature hairline and this is not genetic balding but a normal process. You, of course, want to make sure that you are not balding.  That is why I recommend mapping the scalp for miniaturization so that you will have an idea over what is actually going on beyond what your eye can see. Clearly, you need to know if what you see is genetic balding and the mapping will give you that information aling with a Bulk Measurement which is close to 100% accurate in detecting what you eye can not see.The best solution, is to get to a good doctor who will tell you from proper measurements and a good thorough examination what is happening to you. If you have genetic hair loss, Propecia/finasteride is the way to go. I’d look into medication before considering surgery. If you only have an early appearance of a maturing hairline, then once you ruled out balding from these tests, you can relax and accept a maturing hairline.