Keep in mind, older preset light sets may not be correctly adjusted for current Poser versions.  Another thing that just came to mind, evaluate all your diffuse_values for every single prop/actor in your scene.  As a habit, many vendors set those values to 1 (100%) which is unrealistic and incorrect.  The recommended approximation should be 0.8 (80%) with variability from texture to texture.  I have seen approximations as low as 0.7 (70%).  Shiny metals have very little to no diffuse value, just very high specular.  These adjustments will have an impact on your render time, especially when you start incorporating IDL into your scene.