Since clang15 is going to be branched in July 26, and C++ modules still lack an update on ReleaseNotes. Although it is not complete yet, I think it would be better to add one since we've done many works for C++20 Modules in clang15.
@iains would you like to check if the list is complete or not? I don't include D126694 since I feel like it might not be possible to be landed in 3 weeks. I know there some other patches not covered, but I feel it might be noise to our users.