You are 15 give yourself a break. Many famous composer did not compose, or published their first work until their 30s. I don't know how much training you had in composition, but just because you been playing since you were 6 doesn't mean you will be able to compose.
There are PLENTY of skilled musicians who cant composed, but just play their instruments. My advice to you is, give yourself a break. Keep composing your music, once you get old enough to go to college, go to a music college, and focus on composition if thats what you want.
Bring in things you have already composed, and make them better. You are still young and should not be getting depressed over such things when you still got a lot more time ahead of you.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.