lags after change of anti aliasing

When changing anti aliasing up or down whether its from 4 to 2 or 16 to 2 the game lag to under 5fps for a good 5-10 seconds then will come back to normal fps 

 

 

(Pc specs: 8th gen i5, Gtx 980Ti 6gb vram, 16gb ddr4 ram, 500gb ssd, windows 10 pro)