If you're using Photoshop, you need to go to Edit/Preferences and uncheck a few things, such as saving a thumbnail and ICC profiles and maybe something else. I don't have Photoshop on this computer, so I can't be more specific. Other things that can be done are reducing the JPG quality or switching to GIF.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon