It could be normal for the 15 year old. Only a dentist can answer this after doing an exam including X-rays.
Is it normal to be 15 and have a tooth falling out? It feels lose and I also having another tooth growing behind it, but I feel as if it will grow in the wrong place.
My sister had Cystic Fibrosis as a baby and the doctor told my parents IF she lived, she would never have hair or grow teeth..... God healed her of the cystic fibrosis (wonderful story if anyone wants to hear!) and by the time she was two her hair had grown so long that she was sitting on it! I remember my mom couldn't even put her hair in a pony tail cuz it was too thick for the band! Anyways..... She also got ALL of her teeth and I remember her being 18 and the dentist had to remove a baby tooth she still had. Echooos is right, see a dentist for sure. I just wanted to tell you a story of my sister still having a baby tooth at 18. :0)