on my windows 10 (Redstone version) cortana is using 1-10% CPU Time (webcam microfone activated), and reported by latency checker measured different cpu-latency (on network driver) like Search Assistant “ok google” service for chrome browser. (Cortana works especially if they can hear something )
More Information fixing different CPU/Memory usage on windows 10
(see point 7 ( This option is no longer possible after the update next month))