The more Trunking Sites the slower the Scan.
The more the Frequencies the slower the Scan.
Setup your Favorites List and only have a list turned on when you are in range to hear it. This keeps your scan cycles much smaller and faster.
There are reasons I have over 20 Scanners Operating at home I have scanners setup to hear 1 County only that covers 10 Scanners 1 Scanner for Jackson THP 1 Scanner for Memphis THP 1 Scanner for Nashville THP. You get the idea.