full system scan very slow

Not sure if this is normal or how often i will perform a full system scan, but I have taken 1hr and 45 minutes to scan 15% of my computer. Could someone please let me know if this is the way it is supposed to be and how often I will have to endure this type of timeline. Thanks.

I very much doubt that is normal. A full scan (I’ve only done one; the others have been quick scans) with me took 12’50" for 49.3Gb.

What is your OS, computer RAM and CPU,what other security software is installed, and what AV was installed prior to Avast?

Have there been any malware/virus symptoms? How long have you had Avast installed, and what version of Avast is it?

Have you changed any of the default settings?

Whilst this seems very unusual, without knowing more about your system as Tarq57 mentioned and how much data is on your hard disk to be scanned.