What are you using for point clouds? Leica Cloudworx lets you set the point density and crop out points into areas. When our models start to slow down, we tend to break out the point clouds into areas as we do for drawing xrefs. Even then, it can be slow. There are other Leica solutions and workflows that can speed things up in the CAD world.

Also, if your 16GB ram is correct, that is a minimum for basic cad. If your getting into 3d, you should have at least 32, and point clouds should be as high as you can get it, but a minimum of 64