Full scan used to take about 1:08:00 to 1:20:00, now taking almost 2:00:00???
Did you change any default setting in Avast? Have you added or changed anything in your machine (more for it to scan)? Do you notice a change doing a Quick scan?
Have not made any changes, and yes quick scan is running slower also.
Are your scans coming out clean? Have you done an Avast boot-time scan recently? If not, please do one. I would also recommend that you also update first, then do an MBAM (Malwarebytes) scan as well and cut and paste your results in your next post http://www.malwarebytes.org/. Remember with MBAM to “remove selected” button to quarantine anything found. Thank you.
It’s clean, just scanning slower. Boot scan and MBAM both good.
Same thing here. I “did” add Online Armor Free. Even before the new addition the scans were getting slower. Mine are not as drastic as the OP but were getting slower.
I am so sorry. The persistent cache is still building and the scans are slowly getting quicker. 8)
That may have been my problem also, Today quick scan 11 min, full scan 226.7 GB in 44 minutes! 
If you are like me I need to learn patience. I takes time to build up the persistent cache but it’s worth it. My scan times are getting better, much better. I had one scan which took 49 mins. another took less than 26 mins. So they are getting better. 8)