I tried it on Windows and editing seemed to work fine. There is around 5 seconds delay with the Draw tool, but not 30-90 as you reported, and slice changes and 3D view are responsive.
For me memory usage didn’t go above 2GB, but when I saved the segmentation to file, it went up to 10+GB and it was indeed slow.
Your image seems quite large resolution (0.211 x 0.05 x 0.05mm) but hard to tell without the master volume. Try subsampling them like this:
Also the segment ‘Pontine Nuclei - Right’ is very fragmented, maybe it causes slowdown with
operations like surface conversion. Smoothing won’t help this one but you can make it solid.