It's a bit weird because if you don't call with AK, you're only calling with KK... kind of.
AK is ahead of everything but a boat or super unlikely
[6d] or AA (I don't think a 21/15 calls a raise with A6s or flat calls here with AA giving the blinds great odds). If you have opponent on 88 or 66, you pretty much need KK to call.
But it is hard to make sense of this line. Calling a flop bet and then raising on the turn screams monster, but why just call the flop in a multiway pot when there's a flush draw out?
If you're going to level it a bit, this does sort of seem like a strong draw, like
[9d]. But then you should obviously call with JJ. So...
Either you fold everything except the nut full, or you call with an underpair to the board.