What is the scale your working with? It sounds like you're dealing with very small objects? If so, are there other objects in the scene very far away or very large? That may contribute to the problem. Why do you need the camera to be so close to the object and its shadow?
I deal with architectural projects of various sizes; and very seldom are the shadows a problem like you describe. If and when they are, and I need an image of crisp shadows, I do not use full shaded display; I render in Vray. It usually takes as little as seconds to render the image.