I would 3bet pre.

I don't hate the flop lead though, given UTG is a whale type and we want him calling down his nonsense hands.

If button had folded flop then I think calling his turn shove is close. But with your lead, button still in and he's still shoving, its pretty strong.

A fish can have 24,34,45,46, A4ss,K4ss, any suited 4xss really. A fish can even show up with JJ+ here or some ridiculous overpair nonsense.

don't think folding the turn is too bad with button still in as well.