Can your wisdom teeth grow in when someone is only 15?

Yes indeed: The maturation patterns of individuals can vary greatly. I have had to remove wisdom teeth that were fully developed as early as 13 years old.

Yes: Yes. See an oral surgeon to determine if you should have them removed now or later.

Wisdom teeth: no hard and fast rule, my own sons came in at 15...

Of course: Wisdom teeth are the last erupting teeth between the ages of 15 and 24. I have even seen some 14 year olds getting problematic wisdom teeth in. See an OS for evaluation.