yea its too late, youre pretty much screwed...

not really, 15 is not that old, you still have the rest of high school and im sure you'll be able to put together a band in college. from reading your post it seems you have the talent all you need to do is work at it. just make sure you play and sing a lot, like 2 hours a day atleast. but make sure your having fun doing it, dont just do exercises, i probably practice about an hour a day and then just play around for who knows how long. also, play with your friends and and im sure theyll help you out