We use the tool "Manage Tile Cache" in ArcMap 10.5, for ArcGIS Server 10.3.
The help says: "For the fastest tile creation, your CPU should be working near 100% during the tile creation"
Having 16 cores CPU, and using ParallelProcessingFactor 100% or 16
the CPU usage is very low - between 3 to 8 percents
Any help will be greatly appreciated.