Follow the guidelines described here for best interoperability between Revit and Showcase.
Should you experience performance issues in Showcase while working with your Revit geometry, consider combining geometry in the Showcase Organizer to reduce the number of objects. It is best to do this once you are sure you will not need to re-import the data from Revit. Updating and re-importing data that has already been combined in Showcase will likely result in many visual issues.
Another alternative is to break the Revit model into multiple parts and import them separately. For example, export a building view that has everything hidden except the first floor. Then export a view that has everything hidden except the second floor, and so on. Then you can optimize each file in Showcase before importing the next.