The 15 year old is definitely a minor, and the 57 year old is definitely a pedophile. Anyone who happens to encounter such case should turn the adult to the nearest authorities. Or if you live in the USA call 911 immediately.
It is always against the law for an adult to have sex with a minor. Even if the minor consents to having sex or wants to have sex, it is still always against the law and the adult will go to jail.