18/15 is just really tight.
His range QQ+,AK i would say with no bluffs.
You can do the math to see if its +EV stackoff, prob pretty marginal.
But becomes +EV fast when you include a few bluff combos.

I would prob flat vs the 4B IP yes.

Maybe this a silly answer, but could you look at your PokerTracker stats on the SB and see what his 4bet % is? If he is only 4betting KK/AA then you might prefer to flat or even fold. If he has some bluffs mixed in, then I guess it depends on how wide the range is. Flat the 4bet unless his range is so wide that a shove is profitable. I'm not claiming to have the right answer though, just wanted to start contributing and thinking through some hands with other people.

I would fold to the 4bet. Depending if the fish is positional aware or not, but fish range is fairly strong since he opens utg, your is rly strong because you decided to raise the guy who raised a rly tight range.. Then this other fella comes along and flat which is also considered to be rly strong. Why would someone want to 4bet here light for value / or bluff a lot when he's facing 3 really strong (and live) ranges.

Without knowing the player, but it makes a lot of sense for the pro shortie to flat aces or kings here to not isolate the fish out of the pot. With that said you should know the guy better than me, and I dont play FR fwiw.

Yeah, I'd fold to a 4bet too. Like sweet16 said: UTG has a strong range because he opens from UTG, you 3bet him which makes your range very strong, a guy coldcalls your 3bet which makes his range very damn strong, and then another guy 4bets after that! How strong his range is? If I had to give a rank between 1 and 10, I'd say 11. He has to have like pocket jokers.

Fold to 4b usually.

Your own nitty stats count against you a lot here. That's a key reason why playing more hands is beneficial.

Yeah +1 to fold to the 4bet here.

I am flatting QQ against UTR raise lately, exactly to avoid spots like this and to go into profitable spots post-flop. But if UTG opener is a fish, raise is probably better - depends what is his UTG open percentage and what he does to 3 bet. Usually they call 3 bet OOP to much, so I would 3bet bigger with no blufs.

As played I think jamming QQ against very tight SB 4 bet is -EV. Calling just to make a set is also not justified, so fold is probably best (as exploitation of SBs too tight cold four bet range)

If we're planning on folding QQ to a cold 4, wouldn't it be better just to call vs UTG pre-flop?
That's definitely my default play in these positions with QQ.
I guess if UTG is a fish, 3-betting is probably fine since he's most likely opening the same ~30% range from all positions.