speed up printing dwg w/raster attachments to pdf

i have a few dgn files with hi-res pdf raster attachments (location maps) I can't knock the resolution down of raster files becuase they are large maps of entire counties and the text gets washed out. Likewise I also tried to crop only the portion i needed with photoshop and the text still gets washed out in the conversion.

 Attaching the pdfs and clip bounding provides great results, but when we go to create pdf files of the dgn with the rasters, they  take an exhorbinant amount of time to spool ( ~1hr). Is there anything i can do to cut this time back considerably?

 

Thanks.