GPU usage goes from low to high when i play or test the game in editor!!

so i just started working on a new project and when iam in editor the GPU usage is at 10ms and the fps are from 75fps to up but when i test the game or play it in editor the GPU usage goes from 10ms to 40ms and the fps goes from 75fps and more to 30fps and less and i just dont get the problem cuz if i play another level that has more assests in it nothing happens and the GPU usage and fps are just fine but when i play this world everything just go down but when i exist the play window everything is just fine again…so why when i play in editor the fps goes down and GPU usage goes very high?? i realy could use some help over here…and is this a bug or what?