I just solved this
I disabled Sophos antivirus on the mac, and the horrible performance in windows when accessing folders shared by the mac vanished!
I have all of the mirroring options enabled (desktop, downloads, documents, pictures, movies, music), and I also enable sharing of my users/<my name> folder on the mac. I tried excluding access to users/<my name> but the problem persists until I turn off "enable automatic scanning for maximum security" in the Sophos Home website that configures my local Sophos application
I tried first doing the virtual drive cleanup and that accomplished nothing
Hope this helps someone
