I currently play a lot of Fortnite and so yes like any xD
Anyway, sometimes it happens when I play that my pc goes into "slowmotion" so to speak, it just gets extremely slow and the sound is also extremely slow
I have i5 6400 3,6ghz with 4 cores
A gtx 750ti
16GB ram
Unfortunately, I do not have a direct solution to your problem, but I'm surprised how you try to gamble with an office graphics card ^^
Check the temperatures.
Well the 750ti is on low settings through out for gaming usable. Clear 4k or FHD I would probably leave but you can gamble with it
Is your video card driver up-to-date?