Frame drops while using UE 4.15.2

I am learning on UE 4.15.2, my framerates are being dropped (120 fps(8.33ms) to 60fps(16.5ms)) inbetween the session.My laptop specs are i7 7700hq,Gtx 1070(8Gb),16 gb ram.I expect the for the solution and a possible reason quickly.Thanks in advance.