The problems we were having with the installers turned out to be because SU2016 changes the way it searches its directories for plugins. I've rebuilt the installers with the folder locations fixed:
Octane Render for SketchUp x64
Octane Render for SketchUp x64 (Demo)
These are built for SU 2016 by default, but you can still use them with SU 2015 by changing the install folder.