A chess clock style shot clock might be good for 9-ball:
Give both players 3 minutes per frame, which keeps ticking down whenever they are at the table. once that 3 minutes is up, every shot afterwards will be on a 15 second shot clock. This could result in faster matches than the typical 30 second shot clock with one extension, while also allowing longer thinking for critical shots.
For example, if you pot one ball on the break and continue to break and run from there with avg. 20 seconds per shot, you'd still have 20 seconds left on the clock by the end of your run. But if you play slower, or there's safety exchanges, you'd eventually have to shoot the rest of your shots in max 15 seconds each, speeding up the game and making those 10-15min frames less likely.