Live 1-1 PL hand

A hand from a session last night at the casino:

My stack is about 100bb deep. The straddle is on for 2bb.

I limp behind several limpers with JT in late position.

Flop is A, Ks, Xs, and everybody checks to me, I check through.

Turn is Qs. It's checked to me again, I bet 10 bb, about 1/2 to 2/3 of the pot. Everybody folds to MP who calls.

River is a non-spade 9, MP leads for 15bb, under 1/2 pot.

Should I be scared enough of a flush to fold? These guys in general play any two sooooooted. He was such a passive player that probably with a hand that I can beat (like two pairs) he would not lead this river after check-calling the turn?