More system specs and details:
Motherboard - make and model?
CPU
RAM (make and model) You mentioned both so I understand that you have 2 x 8GB modules installed. Matched set kit for dual channel use - correct?
Drive(s) make, model, capacity, how full?
PSU: Make, model, wattage, age, condition?
Attached peripherals
Network connection: wired, wireless
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If you boot into Safe Mode - does the memory usage change?
Reference the motherboard's User Manual to verify that you installed compatible RAM and that the modules are installed in the correct slots.