I trying to use the resource of multicamera like I always did (with some lags, but workable). My notebook was formatted recently after installing 240gb SDD. It made everything better and Premiere Pro starts faster than before. But my problem is work with big lags on multicamera preview, because it's impossible to watch the takes and switch them.
I work with Full HD videos only. I tried with 'software only Mercury', GPU (CUDA) and GPU (OpenCL). It didn't work. I deleted cache files, reseted my preferences, turned preview setup to 1/4 and 1/8 and nothing works like before.
Your system barely meets system requirments for a single stream of HD. However, if it worked OK before, my thinking is that you might not have the right GPU drivers installed on this fresh drive. You can run Help > System Compatibility Report within Premiere Pro. If that tells you anything about your GPU, you can you try a clean reinstallation of these drivers. Please let us know what happens.
The System Compatibility Report doesn't present issues. All graphic drivers are updated. Although my notebook is weak to work with many resources, I used to edit videos with multicamera, warp stabilizer, lumetri color and the lags were not a big problem. But now preview runs 2 seconds and starts to break. Sometimes shows yellow target with "media offline" and after returns to normal.