to answer this:
The results of the new scan should appear in 15 minutes ??
Active scanning queries the domaincontrollers for computer logons and immediately adds them to the queue when a new logon is found. (this lookup process runs every 10 minutes)
A computer is only scanned once (at maximum) every 8 hours (unless triggered by lsclient or lstrigger)
If you start the service with active scanning enabled, the first scan will look for computers logged on in the last hour.
If none of the computers in the OU contacted the domaincontroller today you won't see any results in the next 15 minutes.