I want to add this for OP (which is definitely bordering for r/relationships advice but my heart truly does hurt for him):

Kid, none of us are hating on you because you’re fat. You’re a stubborn as shit teenager and as most of us are adults watching you react like this, it’s just hard to watch yourself dig your heels. And while you probably won’t be dead at 20, you might think you are fine now and say “obesity isn’t as bad as everyone says”, but you’re 15. You’ve barely lived 1/5th of your life. And, you are on medication for heartburn and experienced a heart attack. At 15! That is not medication they hand out all willy-nilly to 15 year olds who haven’t experienced a heart attack.

We just want to shake the truth into you before your life gets to a point of indignity. I empathize with you, kid, I can see exactly where you’re coming from. But resisting these efforts is not going to make your life better down the line. You may have won the battle, but like this, you will lose the war.