AutoCAD LT :: Slow Layers Properties Manager?

I am using AutoCAD LT 2013 where I work.I am working with a Floor Plan in which the building and the Site Plan are XRefed and the drawing is very slow.

The building is small, but the XREfed Site Plan, being of a large shopping center, was as drawn by a survey company, and is large.  I took out (erased) the solid hatches that indicate the concrete, to make the site a little smaller.  Since I do not use the entire site plan on the recipient Floor Plan Sheet, I clipped it using XClip, so only the necessary areas and parking around the building are shown.

I notice that the recipient drawings are very slow (i.e., the Floor Plan where I am working), and the Layers Properties Manager is the worst offender, being very slow and erratic when I want to add a new layer, change layer name, etc.

The computer is a new very large computer, and I did not have this slowness problem before working with other prjects.

Is there any setting or some settings that will make the drawings faster?