This is one area I believe as well as many that there should be limits.

Firstly the playing taking so long over the shot is making it so they can harm the rhythm of the game and two is very boring to play against or watch. This is a good reason why cue sports aren’t as popular on tv as some players stuff it for the rest of us.

If you have the opportunity and get a bad draw with a well known slow player as the referee to warn the player if it happens.Better to just ask them before the match as i will be doing from now on as there a well known players in Both snooker and pool that hold world records in time wasting.
If you get someone taking minutes and you have no referee say something to them as they are only trying to do it to harm your game