I'm 15, and my voice has already gotten deeper. But I'm still small so if I grow up, does that mean my voice will get bigger and then deeper too? My adams apple is already big that my friends consistently poke at it XD but i still sound like a little boy.
When you're 15, you're still going through puberty. For men, puberty doesn't end until you're about 16-22. Puberty ended for me when I was 20. Maybe it will mature, maybe it won't, but you still have time for puberty to work it's magic.