My puppy is 13 weeks now and he is only just starting to wake up more easily. He is actually hilarious to wake up... he won't open his eyes, he wimpers, snorts and stays totally limp. It can take a few minutes to get him fully awake.
As long as he is eating well and has lots of energy when he's up, I wouldn't be alarmed. Some puppies sleep an astonishing amount- it varies from puppy to puppy. He'll wake up soon enough and you'll want your sleepy puppy back again
If he seems lethargic when up, has a runny nose, vomitting, diarrhea etc, those are all signs that he needs to go to the vet. But just being a sleepy little puppy is a-ok! Enjoy the rest while you can!!!