Left VS2022 going for an hour, by that point it was using 6GB of RAM and was still sat on 100% of one core.
No idea what the hell that thing is playing at (and I can't find a way to tell, and even if there is the UI is so unresponsive I'm not sure I could get to it!), so time to verify the UE5.5 install and the VS2022 install I guess...