Is it really weird for someone to have nocturnal enuresis (night time bedwetting) at age 15?

No it is not. Nocturnal enuresis is a common problem. By age 6, 10% of boys still have bedwetting with a gradual reduction with age. If it's primary enuresis (never dry at night), it almost always resolves with time. I'd see your child's doctor and inquire about an enuresis alarm. They hasten the resolution of the problem in over 70% of kids. He may also check for uti, diabetes, and constipation as indicated.
No. 10% of kids have enuresis at 6 years of age and 10% of them get better with each passing year.