You may try to experiment with different settings for the 3D Window to make it faster. For example, set it to Internal Engine, then set the Hidden Line Mode field to Raster, turn Contours Off. (Leave the Shaded Mode field on Analytic as that is needed for shadows to appear).
Another thing you can do is to save two Views, one with Shadows, one without Shadows. This will save the camera and target points as well so activating them switches back to the saved position, but only you know if that is an OK workaround for you or your purposes.
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