Try purging some layers and stuff that you don't need. Make sure not to have lots of project objects in one single file (surfaces, alignments, profiles, etc), you're better off creating shortcuts, if that was the case.
On the other hand, do you have many poltting styles? How do you have structured you plotting styles and printer configurations? If you had your plotting styles as per project or per ranges, you can just set them to that specific range. You can do this by: Optiones/Files/Printer Support File Path/Plot Style Table Search Path/, then you can select that specific range for the plot files you'll be using. Same goes for the printer configuration path. When you have many styles and configurations set in your path, it make regen of your drawing super slow. That worked out for me.
Give it a try