Looks like CircleCI just added Xcode 15.0.1… and after some preliminary testing, it looks like all performance issues have been fixed!!! 
Update:
Well it seems like it’s not quite at Xcode 14 levels. When I enabled the suite that I had disabled for iOS 17, tests do go from ~8 minutes in Xcode 14.x / iOS 16 / Intel to 29 minutes in Xcode 15.0.1 / iOS 17.0.1 / Mac M1.
The difference is that this separate test suite does require a host app (they’re SKTestSession tests), whereas the other ones run without a host app.
And because of this performance issue, a bunch of tests fail due to timeouts: https://app.circleci.com/pipelines/github/RevenueCat/purchases-ios/15769/workflows/93f0d042-2a60-4b73-af15-54542ab496a6/jobs/134913