It is hard, but if you are really devoted it could happen. Send demos to record companies and see if they respond. Also sing wherever you can, put yourself out there. Sing at local talent shows, join a choir and even put yourself on Youtube. Just be out there and who knows - maybe someone will notice! & How to be a famous writer...? You aren't guaranteed to be famous, you just have to work at it. You have to meet the standards of adult writers and you will have to have the backing of your parents to carry out legal aspects of writing. Being 15, you lack experience in many ways and if you try to write from your reading, you are more likely to produce duplicates of what the editors see every day - and reject. Again, you have to be devoted, goood luck
Make a Youtube video out of it. Maybe several...