To turn off the visibility of a segmentation object entirely, you can use the visibility icon in the Data module. Turning visibility on/off is a very fast operation, shouldn’t take long.
Individual segment visibility can be controlled inside the Segment Editor easily. Again it should be fast. The only time it might be slow if you have the 3D visibility also turned on. If that’s the case, try the new surface nets based 3D reconstruction introduced in stable 5.6. It is very fast, particularly if you also choose to do the smoothing with it. See this New surface model generation method: SurfaceNets - Support - 3D Slicer Community