
"The good news is that this should mean CU15 is being tested more thoroughly than the November 2024 Security Update (SU)"
I wouldn't like to bet on that...
The Exchange strategy has been a complete mess for a number of years - remember that there was no 2022 version either (previously there was normally one released around the same time as each major Windows Server release), There is also still the ridiculous situation of needing to have an on-prem Exchange server to manage mailboxes attached to hybrid accounts, unless you want to use Powershell for every little thing (Powershell is fine for bulk changes, but too much hassle to use it for every minor change). They could easily have released a lightweight GUI-based management tool for this, with none of the mailbox hosting or transport functionality (it could have been part of RSAT, even). But of course they haven't and are showing no signs of doing so.