We'll certainly need more context in order to answer your question appropriately.
- Is it simply a pool hall with members e.g. a in a retirement community or fraternal club, or is it an organized pool league?
- Can you give us a feel for what "extremely slow" looks like in this case? Are we talking 60 seconds before executing a shot, or are we talking 2 minutes?
There was some research and accompanying white-paper released in 2010 by a billiard shot clock app company, Performance Accountability, LLC, which seeks to answer the question "How Slow is Too Slow? What is an acceptable playing pace in amateur pool?".
Here are the relevant sections of the World Pool-Billiard Association rules around "slow play". This, of course, requires a referee or officiant. This applies to 8 ball, 9 ball, etc.
6.15 Slow Play
If the referee feels that a player is playing too slowly, he may advise that player to speed up his play. If the player does not speed up, the referee may impose a shot clock on that match that applies to both players. If the shooter exceeds the time limit specified for the tournament, a standard foul will be called and the incoming player is rewarded according to the rules applicable to the game being played. (Rule 6.17 Unsportsmanlike Conduct may also apply)
The "Unsportsmanlike Conduct" is for when the referee has asked the player to speed up play, and the player ignores the direction and continues with slow play. In this case the specific unsportsmanlike conduct is called:
g) delay of the game
So in summary, if an official deems there to be "slow play" occurring, he or she may impose a shot clock, to which all players must adhere.
Update 2021-11-29 - This morning I found a funny related cartoon in an January 1994 issue of National Billiard News and thought I'd share it: