Increase shadow rendering speed in mental ray for Maya

To make shadows render faster, do any of the following:

For Maya software and mental ray for Maya, use depth map shadows instead of raytraced shadows.
For surfaces that do not need to cast shadows, turn off Casts Shadows.

To make depth map shadows render faster, do any of the following:

Set the Resolution to the lowest value that produces acceptable results. (For shadow casting spot lights, first reduce the Cone Angle to the lowest value that produces acceptable results.)
Turn on Use Auto Focus (or set the Focus to the lowest value that produces acceptable results. See Focus, Width Focus) and set the Resolution to the lowest value that produces acceptable results.
For Maya software rendering, set the light’s Filter Size to the lowest value that produces acceptable results. A Filter Size value of 2 or more is usually sufficient. For mental ray for Maya, adjust the Resolution, Samples, and Softness settings under the light’s Shadow Map section.
For Maya software rendering, Set Fog Shadow Samples to the lowest value that produces acceptable results.
For Maya software rendering, set Disk Based Dmaps to Reuse Existing Dmap(s).
For Maya software rendering, if a point light does not have to produce shadows in the light’s positive or negative X, Y, or Z directions, turn off the appropriate Depth Map Shadow Attributes : Use X+ Map, Use X- Map, Use Y+ Map, Use Y- Map, Use Z+ Map, or Use Z- Map.
For Maya software rendering, if the scene contains NURBS surfaces, in the Memory and Performance Options section of the Render Settings: Maya Software tab, make sure Reuse Tessellations is on (the default setting).

To make raytraced shadows render faster (for Maya software rendering and Maya hardware rendering), do any of the following:

If the Light Radius (or the Light Angle for directional lights) is greater than 0, set Shadow Rays to the lowest value that produces acceptable results. See Shadow Radius, Light Radius, Light Angle for details.
Set Ray Depth Limit to the lowest value that produces acceptable results.