I have the same issue. Clean Windows 10 64 bits installation on an old Intel Q9550 8GB RAM PC, latest rawtherapee 5.2 downloaded from main site.
I haven’t the floppy disk A.
Using process explorer it seems to consume very low CPU time, but memory increases from 37MB to 156MB.
Not much I/O activity, some peaks here and there.
Every execution needs 3:45 minute from launch to windows show.
Settings windows needs a couple o minutes as well to show!
In settings, when I click on a setting requiring the folder dialog (example: start folder), the dialog needs more tha a minute to show.
The same from a click on a thumbnail to edit window.
Everything is delayed and slowed. Unusable.
Hope the developes can solve this issue, I love RT.