Catalina slow too boot, change users

Installed Catalina 10.15.1 on my 2019 3.6 GHz Intel Core i3 with 8 GB memory, and it is extremely slow when logging into my user account or when changing users, maybe 10-20 seconds after entering password before login complete. I checked the memory tab in Activity Monitor as shown below. Is there anything I can do to make Catalina work better? On the other hand, how can I get back to Mojave?