Some of the advanced tessellation parameters can dramatically increase rendering times.
Because the tessellation of NURBS surfaces has nothing to do with the material assigned to the surface (unless the surface is displacement mapped), you can start adjusting tessellation early in the process, anytime after the object is modeled.
To adjust tessellation on NURBS objects
If you want to apply settings to All surfaces, skip this step.
Fine-tune the adjustments you’ve just set until you reach an adequate level of smoothness.