Might be of use to someone else...
I found installation using Setup.exe took too long.
I extracted Setup.exe which provided the following files;
mike@mike-laptop4:~/Downloads/rs5-pol$ 7z e ../Setup.exe
bla bla bla...
Everything is Ok
Files: 4
Size: 1335973325
Compressed: 1321246056
mike@mike-laptop4:~/Downloads/rs5-pol$ ls -1
setup.exe
SK-POL-L1-NA-PE-NA-NA-Y-3.7.5.2.r2.rsd
SK-POL-L2-NA-PE-NA-NA-Y-3.7.5.2.r1.rsd
SK-POL-L3-NA-PE-NA-NA-Y-3.7.5.2.r1.rsd
using the extracted setup.exe installed much faster (RS then seems to extract the rsd one by one migrating them from an "Autoinstall" dir to "Content" dir).