I have found that having the nesting link on in the XRM even when there are no nested xref's slows things down considerably. If there are no nested xref's in your xref then try toggling off the nesting in the XRM. There are also a few stone or rock hatch patterns that we avoid like the plague due to the slowness of the regens. We are still using DC15 here but this seems to be another problem that has carried forward and needs to be addressed. Good luck with this issue.
Have to assume this is still an issue for a number of users? I use a lot of x-refs as well as hatching so I realize I am playing with fire : ) and my suspicion is that this also has to do with networked printers/printer drivers but it can be very frustrating to deal with - especially since we can't draw in "paperspace" as is possible in autodesk products, microstation, sketchup etc...
We've made some improvements in this area in DataCAD 19.
"A new key, New Check For Nested, has been added to the [XREFs] section of DCADWIN.INI. If set to TRUE, the default, new trivial rejection logic is enabled to ignore nested XREFs if nesting is turned off, either for the parent XREF or globally. This will reduce the amount of time required to process XREFs for display, plotting, and object snapping."
You could try the demo version to see if it makes any difference in your case.
Are you using a lot of XREFs, or a lot of Self-XREFs?