[_Sundance]

My thoughts fwiw:

From your read of UTG I guess much of his range after his flop check is AK/AQ. Button could have a wide range here and your only read suggests he might be aggressive. So, it's unlikely the next card will put you behind, it could improve UTG/button and button may bet - so some positives for slowplay. However, UTG may not stack off if he improves with AK given your read and if another H comes it could either kill action or be difficult to build massive pot even against the flush with a paired board. Also, you have a LAG image so your hand is more disguised. So I would bet about $70 on the flop - flush draws may call given stacks.

Turn: Given your read, UTG now has either a lone big H and is trying to pick up the pot cheaply or hopefully a flush (less likely). Button doesn't seem interested in the pot. Time to bet here. UTG may figure his flush draw and 2 overs are all outs so you can bet accordingly - make it $150 giving him $100 to call into a $300 pot planning to push any A/K or H river and make a smallish bet otherwise.

River: Given his river call the button has something - my guess would be another big lone H. When he raises the river here I think as likely to have 66/Ah than JJ/44/53hh here. I raise all-in.

So your slowplay worked in a sense in that you allowed UTG to improve and got his stack in. However, you could probably have achieved the same result with at least a turn bet. Even if JJ did call that then you are probably still long term +EV.