Here is what Autodesk suggests about importing DWG files into Revit:

1. Minimize the number of linked or imported DWG files.

2. Avoid importing unnecessary data like hatching or AutoCAD®-specific linework such as construction lines. Delete unnecessary parts and layers of the DWG file within AutoCAD and import only the cleaned, smaller DWG.

3. Avoid exploding the geometry imported from DWG files. The exploding operation within a Revit-based application can change a DWG from a single managed element to hundreds or thousands of additional elements depending on the number of entities in the imported DWG.

4. Only link essential DWG files into necessary views.

5. Switch off visibility of 2D AutoCAD DWGs in perpendicular views. A 2D AutoCAD file linked into a plan view will show as collinear lines in elevation, causing performance degradation.