There are a couple of possibilities for the lag problem. Are you using the Organizer? If so, and have loaded a large catalog, the media analysis can be a resource hog. Try turning it off in Edit>Preferences>Media Analysis.
Another (random) possibility is if you have Acronis True Image installed on your computer. In the past, I have found it interferes with the operation of ACR. Elements needs to be excluded from its scan.
It is not possible to downgrade ACR for use in Elements.