In P9 and PP2012 HW Shading has improved dramatically and has been turned on by default. In the original released version it had as a side effect that after a render all textures had to be reloaded and recalculated. To speed this up in SR1 they used the (render) texture cache.

If you turn it off in the ini file (KEEP_OGL_TEXTURES_LOADED 1), I think it will go the original way (not using the cache for HW Shading) and will be slow again when changing modes. But to get back the speed of PP2010 you can turn Off HW shading in the render settings for the Preview mode. In PP2010 it was default Off

It is a simple experiment - edit the poser.ini when Poser is closed. Then restart Poser. If Poser is still open when you edit the ini file, the ini file will be overwritten when it is closed