I think since you're IP preflop $12 is ok, $15 is also no mistake.
On the flop:
Board: Ks 3s Th
Dead:
equity win tie pots won pots tied
Hand 0: 39.970% 32.71% 07.26% 77094 17108.50 { KK, TT, AKs, KQs, QsJs, AKo }
Hand 1: 45.445% 42.21% 03.24% 99472 7633.00 { KK+, TT, 33, AKs, AsQs, AsJs, AsTs, As9s, As8s, KQs, KTs, QsJs, JsTs, Ts9s, 9s8s, AKo }
Hand 2: 14.585% 05.70% 08.88% 13443 20932.50 { AcKc }
you can fold imo.
I already included a lot of draws so your equity might even be slightly worse.
MP is a reg so he's not doing this as a bluff, he always either has a monsterdraw or 2pair/set.
Edit: I just saw that i mixed up the position so the ranges above may not be 100% correct, i thought UTG+1 was the reg.
But the result should be similar if you adjust the ranges, it doesn't affect the decision to fold.