When I first installed the link scanner edition, it was literally taking up to minutes to complete loading a google search web page on firefox. It was quite clearly from the software as I could see each link slowly loading an icon indicating whether it was acceptable to AvG. They may have changed this based on complaints; I wouldn't know as I disabled that feature promptly and was back to my expected speed of down/uploading.
It's possible that your scan only takes 20min since you are only using 7G occupied; when I mentioned 80G+ drives, they are up to 90%+ capacity (at least the primary is). Those camtasia files hoard an awful lot of space (One of these days I will just send them to dvds for archival storage as they are cheap). I think when my hdd was that low on occupied space, AVG was a lot faster, so my guess is the dramatic time increase is indirectly proportional to % of drive occupied and files to scan.
Haven't tried the OPs suggestion yet, but will sometime.