I’ve reduced number of vcpus in service qubes and I’m using 4 vcpus in YouTube qube - I have way less powerfull cpu, i5-1245U with max frequency of 4.2GHz observed in QubesOS (normally it goes to 3.9).
You could chceck if disabling turbo mode will cripple your cpu (as mine goes bellow 1GHz) or it improves battery