Cronjob that checks every 15 min if there is no APM active session, than disable the virt.

Looks like you got it working, just wanted to add that a periodic iCall may be a better fit if this is a long term solution because it would: 1) Be replicated to non-master blades (if using clustering with VIPRION) and 2) Sync between devices in a DSC group, persist upgrades, etc.

Dan