First one I got was 15 and a half, at this youth thing. Felt sick, and there was a tiny bit of blood there. The next year, I did a HELL of a lot of running, 50km a week, and I competed in the 3000m. Basically as other people have commented, this makes it go away/be less frequent. I didn't have any more at all until the end of the next year, at a camp, but it was light. Anyway, then it started going "normal", and these would get me so down mentally my mum said to me about going on a contraceptive, instead of me asking. While at the doctors getting it I also asked about the FTM process, didn't plan to come out, but this gave my mum about 6 months before I "properly" came out.
This year, I get progesterone shots every 12 weeks from the school nurse. You don't even have to tell your parents about it, since they give out condoms and contraceptives at highschools ( atleast in my country ) and also, nurses tend to be in charge of the student LGBT support which is definitely awesome. I still get breakthrough bleeding in the last 2 weeks, but atleast I can go to school - with periods I do not got to school, because I get so bad. Pretty low attendance. Anyway, try to get on that. Also, progesterone is not oestrogen, so you won't speed up puberty, but you do get hungry/gain weight but that doesn't effect me since I do a LOT of exercise, which also helps with periods and your mental health.
Otherwise, try do some cycling, indoor exercycles are also perfect - dont have to wear a binder - or running, plus weights will help with your shoulders and arms at the same time.
Good luck, and man, I know what you're going through :|