AK in $11 Multi - 19 Left

19 left in a PS $11 tourney. Blinds at 6,000/12,000. I have 160,000 chips, right at the average, but one of the bigs at my table. I raise to 48,000 from EP with AK and its folded to the BB, who is the big stack at the table with ~270,000 chips. He takes a long time to decide and finally pushes all in. I hadn't been at the table long to have a decent read on him. I make the mistake of checking the payout structure for the tournament and see that 18th is a bit of a jump from 19th. I'm currently at the beginning stages of building a bankroll and the jump is significant for me. I fold. Is this a call I should have easily made and expected to see an underpair for a coin flip? Does anyone fold here? The account building thing weighed into my mind, but taking that out of the equation, easy call to hope to secure a spot at the final table?

Thanks