To reuse a RIP'ed image, you need to have a RIP that has some caching technology, such as Fiery FreeForm, or Creo VPS. Verify if your RIP has such capability, and if so, then in PSM, go to Edit->Preferences, and under technology, choose the proper caching technology.
If you do not have a RIP that allows caching however, the images will be reprocessed on every pages. If that's the case, you might want to try regenerating your images to make them smaller and faster to process. Things like reducing the unused color depth(an image might only use black and white, but if it's saved as a color image, it will be processed as such), image size or, if it's pdf or eps, maybe generate with a different program, lower version, or anything that would reduce their complexity and improve ripping time.
Hope this helps.
Regards,
Rapha