You seem very knowledgeable about the hardware, but I have to ask if anything else is running when you start PhotoLab.
I have a 6-year-old I7 Windows machine with 24 gigabytes of RAM and a small SSD drive that just contains the operating system and my programs. My graphics card is a GTX 1050Ti.
Fully rendering images on my computer after edits are applied takes a second or two below 75% zoom and perhaps an additional second or two at, or above, 75% zoom.
When changing ito another image, full rendering time depends on the size of the raw file, the number and type of edits that were applied to the image, and if the zoom level is above or below 75%. As an example, with 25 MB raw files, changing to an image with no edits takes around a second or two to fully render… Changing to an image with a large number of edits, may take 3 seconds.to completely render below 75% zoom, and as much as 7 or 8 seconds to render at 75% zoom or above. This is because certain features in PhotoLab, like Lens sharpness and the Unsharp mask are not applied to the preview below 75% zoom.
Your larger 45 mp raw files, (I’m not sure how many megabytes each raw would be), would certainly take longer to render on my machine. However, in my experience when occasionally editing higher resolution images like yours, it still usually takes less than half the time to fully render compared to what you are seeing on your much newer and faster hardware. Even when I edit something like a 100 megapixel medium format Fuji raw file, rendering on my machine is still faster than what you are seeing. For me the only major issue with a very large image is the significant extra time it takes when I export it with DeepPrime.
Since very few users on this forum seem to be having similar issues to yours it suggests that something on your computer is interacting with PhotoLab to cause the slowdown you are seeing.