I'm having WiFi issues with my 15 Pro as well. Not necessarily pages not loading, just really slow speeds at times and issues with apps like IG not playing videos all the way through or being able to refresh the feed. Very frustrating for an $1,100 phone.
Interestingly, I also have an iPhone 12 provided by my employer and it routinely runs 3 times faster than the 15, which means it's like the phone itself that's the issue. Both are updated with iOS 17.1.1. I've tried a few things, but nothing has seemed to worked so far.