High game thread utilisation in viewport, stat game doesn't add up

I have a project that is running very slowly in the viewport. Instead of the expected 120 fps, I’m getting slightly over 60.

GPU load is not a major concern right now, but the 13 ms game thread is unexplainable. The game stats don’t add up:

The game thread should be closer to 7 ms, not 13 (with spikes to 18, so I don’t even hit 60 fps in the editor). What else could cause this and how would I do performance profiling on the viewport?