It all depends upon how much file your computer has and how much data does Avast scan in a quick scan. I have some programs that are quite big i.e. Revit, SketchUp, and some big Autodesk programs. All other computer essentials are also to be scanned. Here is my scan result.

Note: This is my 1st time doing a full system scan ever since Avast 2015 was released. I even haven’t done a full system scan when I installed the 2015 version.

Correct me if I am wrong, I think 1st time scan it should take some time to scan the files and by doing weekly scan the scan should be faster.