Can a 17-year-old go to jail for getting a 15-year-old girl pregnant if her parents press charges in the state of Pennsylvania?

No. You have to be 4 years older than her.

See: PA 18 ยง 3121
Rape to engage in deviate sexual intercourse with a complainant who is less than (1) 13 years of age or (2) 16 years of age and the actor is four or more years older.