Hello @georgepickles
It depends on many factors, and how you are exporting. For example, on my system, subdividing the demo soldier to around 33+ million polygons and attempting to save it as a ZTL completes very quickly, exporting to OBJ takes a couple minutes, and exporting to .FBX took so long I just gave up on it.
There may be something else involved with the nature of your mesh and what/how you are attempting to export, but…
It’s high by any standard, including internal ZBrush usage, and most other programs can’t handle the same kind of polycounts Zbrush can. You want to avoid ultra dense meshes whenever possible. Certain CPU intensive functions in Zbrush wont be able to function on a mesh that dense, and the denser a single mesh gets, the higher the potential for performance issues and instability. It’s better to have your polygon load spread out over many subtools if you can, than to have a single ultra dense mesh.
Remember, the display of high frequency detail in other applications is the typically the result of displacement and normal maps applied to a fairly low poly mesh, not actual geometry. If working for print output, you would absolutely need to decimate that mesh to make it usable for pre-print software.