From the tests I've seen it only shaves off a tiny percentage of loading time.. however PS5 is rumored to be much faster when loading from disk and is backward compatible... only downside of course is waiting the 2 years :)
TW3, IMO, is one of the best games on the platform. The loading times do suck but the game is worth it. I played through it 3 times to get a platinum trophy in it.