How can I tell if I'm hitting the 16GB RAM ceiling?

Yes. High page file usage is the main sign. Other signs include game stuttering after a while, frame time spikes not matching GPU load, RAM hovering at 14-15GB, slow alt-tabbing, sluggishness after exiting a game, and “Hard Faults” spiking in Task Manager. An NVME drive doesn’t fix this—page file I/O still introduces latency.