Extension of stay beyond 15 day free in China

It’s possible to extend it, but I cannot assure that it will succeed in the end. You can have a try. You may need to prepare those documents including your passport, the application form, a recently-taken half-length photo, valid registration form of temporary residence, and an invitation letter from your friend as well as the return ticket. After, go to the exit and entry administration of the local PSB to extend it.