Did you wait for the indexing to finish?I’ve owned 8 generations of iPhone. I’ve participated in public betas since Apple offered them. I don’t ever recall my phone running this slow with an upgrade. All on the most powerful iPhone ever…it was an observation on my part that has amusingly and predictably ruffled some feathers.
This current beta seems to perform mostly fine to me, other than a rendering bug on the lockscreen -- though, I queued up the update shortly after it dropped and then just stowed my phone for the rest of the workday, so it was quietly installing and indexing sight unseen. (My employer tends to frown on cell phone use at work.)
Only 7 gens of iPhones, here... and I've likewise been using Apple's betas for quite awhile -- actually, since well before iPhones were a thing, starting with that very first Mac OS X Public Beta, back-in-the-day. The worst performance hit I ever observed was on my iPhone 6, when "batterygate" dropped. Since I was using the beta at the time, I just assumed they would fix it before final release... and then, they inexplicably didn't. That performance hit was immediately noticeable, and didn't go away until I replaced it with an iPhone X.