Relevant versions: 8.0 and up
The priority of the Endpoint Agent is not configurable. The default priority is "Below Normal" for an Endpoint Discover scan. Most applications that interact with users run at "Normal". Endpoint Prevent runs at "Normal" because slower processing would slow down the machine. A busy Endpoint Agent should not slow down user interactions.
With Admin priviledges, you can manually modify the priority of a running process. But since this would have to be done on each machine, it is not a practical option.