You're right, it may be xppc.Agent or xppc.Agent.17.0 too, not just xppc.
The agent is what VS is using. In my case, it doesn't start automatically when I kill it, until I start another build. If you kill it and it immediallly starts again without you trying to run a build, then there seem to be another process doing that. In that case, I would check whether it starts under your user account and whether it happens with closed VS too.