This hand happened at a local live 5/10 game. 

UTG+1 is a solid reg and very, very nitty.

BT is solid player capable of opening from late position with a range of big cards, big pairs and big suited connectors.

My image is fairly solid as well to both.

I limp from UTG with AcJc with 500bbs.

UT+1 limps behind with 300bbs.

BT raises to 60 with 160bbs.

Both blinds calls 60 and we both call.

Flop (300): Kc4s7c.

Everyone checks to the BT who bets 175.

Both blinds fold and I make it 900 with my nut flush draw.

UTG+1 goes insta allin for almost 3k.

BT goes insta allin for about 1.5k.

Action goes back to me. Should I fold or call the last 2.1k?