There might be something fishy going on, yesterday a user posted something similar, but I thought regarding all his replies that it was 100% user fault (he was saying Nvidia breaks all the time on his system, said he never installed 5.15 RT himself) see this thread Black screen of death after update - 515-rt & nvidia drivers - #56 by omano
There was also this thread but the user tends to take time to respond Kernel 5.15.13_rt26-1 not booting on my laptop for audio pro usage and another user linked this thread Boot to black screen after recent update
With this thread here it starts to make a pattern. Just reporting this here as this may be something to look into.
//EDIT: I will experiment myself, and see what I can find wiith the 5.15 RT kernel with Nvidia.