I don't think you should push the flop. I think you should call his flop bet and see what happens on the turn.

it's a tough spot. it's unlikely he has pockets. if he bets 15 into 21 on the turn you have a difficult decision to make. i think you should just call the flop and see what happens on the turn. You are giving him a free card, but I think it's better to keep the pot small. also, you give him the opportunity to continue bluffing with overcards. if you push - he calls when you're behind and folds when you're ahead. he might fold 88 and 77 if you push and might fold 22-66. but in general, a call means you're behind.