Can a 15 year old join and participate in the activitys?

Yes!

Hello! Thank you for reaching out! You can join PF starting at the age of 13 with a parent/legal guardian’s permission; they must be present with you during the sign-up process. Members who are 15 to 17 years old must have a signed waiver from a parent or guardian on file. Please note that any PF Black Card® guests must be 18 years old with a valid ID, unless they’re accompanied by a parent or guardian.

I think they have,2b with an adult