Having upgraded from 2017RC to 2017 in most regards 2017 is now installed, but Explorer still has 2017 RC as the Open With… option.
It may be due to this, or unconnected, that when opening "15" .sln files 2015 is still favoured over 2017
uninstall visual studio 2017 rc
python not showing in installer
Upgrade VS2015 Community Edition
Install sticks at Applying GitV2
Installation directory not respected