successfully got 5.15.2 to boot after patching linux-zen with the patch from Re: [REGRESSION][BISECTED] 5.15-rc1: Broken AHCI on NVIDIA ION (MCP79) - Marc Zyngier and 3 patches from [PATCH 0/2] PCI: MSI: Deal with devices lying about their masking capability - Marc Zyngier .
looks like these patches are included in linux-mainline 5-16-rc1, which boots without issue as is from the repo. hopefully this is all a thing of the past soon enough.
thanks again for the assistance.