The reason why performance drops off so much is because of the very high memory utilization. When memory utilization is around 60%, Windows starts moving parts of memory to the virtual storage paging file. It will continue to move memory around until the overall memory demand drops. When 14GB is used in a 16GB system, Windows is moving a LOT of memory to virtual storage. Since MSFS uses the most memory, MSFS is significantly impacted.
For MSFS, the biggest, worst performance impact is for memory to start filling up and Windows starts moving memory out to virtual storage. FPS drops significantly because Windows cannot move memory in and out of virtual storage fast enough for MSFS.
The easiest way to “fix” out-of-memory problems is to add more memory. Install 32 or 64 GB of memory. Another possible solution is to not use virtual storage since it is too slow for MSFS. However, Windows will freeze or crash if real memory is totally used.
The real “fix” is to fix WHY so much memory is being used. Something is definitely broken.
Whenever I see Windows start moving memory to virtual storage, I usually stop flying because I know FPS will drop too much.