Right. So my guess is that your iGPU isn't pulling it.
Your footage is H265 which can be heavy to decode. If you enable Smart Cache (top menu: Playback>Render Cache>Smart) you might see an improvement at least when it comes to playback. But I expect you'll continue to have problems as you get deeper into the software.
But short of upgrading your hardware, you might also want to try converting your footage to a more editing friendly format (less heavy to decode). You can grab one of these ProRes sample files from ARRI if you wanna test that for comparison.