Hey,
well by reading your post it sounds like you are just growing right now. At age 15 your body needs a lot of food and feeling hungry all the time is something normal for people your age. After all you are a teenager. So I wouldnt worry about it too much...If you are really that worried maybe you could see your gp but I think you're fine.
I'm not sure if you're a girl. Because if you are it coulad also be caused by the chnages by your menstrual cycle.
I hope this helped, i'm not a dr or anything, i'm about your age (i'm 17) but this is just what I know. Hope I helped even a little. Take care.