It looks like the death toll of workers on the 2nd death star could be fairly low. Quoting part of TenthJustice's answer here
Wookiepedia describes the second Death Star as being primarily constructed by droids:
Methods of faster construction had been developed in the years since
the original station's conception, added to the fact that Imperial
engineers made sure to allocate enough space on the station for the
maximum possible amount of self-replicating construction droids.
Their source for that claim is an official book called Star Wars: Complete Locations
On top of that, according to George Lucas, the first star destroyer was at least built with
...I came up with the idea of adding a little schematic of the Death Star in here, because the Geonosians build robots and build things, they're sort of construction workers. They would probably be the ones contracted to build the Death Star, and they were the ones that Jay and Silent Bob worry got killed on the Death Star, but they are after all a bunch of large termites.
We are not to feel bad for the workers because they are essentially insects that breed in mass quantities. Obi-Won and Anakin also kill them fairly freely in the movies compared to them killing other life forms.