You are 15, quit worrying, you can potentially continue to grow until your early 20s. As long as you don't sound like a castrati, its fine. I have an unusually deep voice (at random times) which just kind of sets on depending on my mood. Then people say I sound like a black guy -_-, and I don't know, I don't think my voice is that great just because its deep. I like it because I can simultaneously change from high to deep, and mess around with asian/indian accents =) I'm working on british... Anyway, back to the normal topic, you have a lot of time on you. Such a thing can only change with time/genes, what you can do for now is focus on other qualities that would make you more masculine, i.e working out. Which by the way, can raise your hormonal levels, which could then possibly improve your growth and voice.