How long does it take to restore from time capsule

I'm have issue with booting my IMAC so I'm trying to restore it. I have a 3TB time capsule and am performing a restore from to the iMac at first it calculated 20 hours to restore but it has been running for 12 hours and only 191GB it now says 41 hours to restore and it continues to grow. I performed the hardware diagnostics and there were no issue reported (actually while running this was the first time I heard the disk spin in months, I'm not sure that has anything to do with my issue). The past few days my system started running slower and slower, I thought it might have been a virus but I use MALWAREBYTES and BUGZapper and there were no virus's found. I was getting the circle with the line thru it for a while before I decided to try to restore. Could this be a hardware issue that the diagnostics software not detect?

Thank you in advance