Ping98,
Interesting situation! The problem could be a couple things, or a mix of them.
# Storage getting full. How much available storage do you have? Windows uses something called Virtual Memory, which you may be familiar with. It uses it as an overflow when the physical RAM is maxed out. However, I find this as an unlikely problem since your configuration says 16GB, which is great for a laptop. Try cleaning some larger files/apps.
# Overheating. Laptops, throughout time, heat up more and more frequently as they age and often times throttle CPU clock speeds to lower the system temperature to a safe range. This is called “thermal throttling”. To see if this is the issue, [http://intel power gadget explained|download Intel Power Gadget], run it, and see what your idle and active operating temps are. You should get idle temps of 30-45 and hopefully under 80 while gaming. If your temps are above these ranges, I would try and clean the inside of the computer with compressed air, or replace the CPU and GPU thermal paste.
Run Power Gadget and let me know what kind of results you get.