Our office does primarily big projects, many of which were started in Revit 2013. When Revit 2014 came out along with the service pack to fix the bugs, we were going to install both Revit 2013 and Revit 2014 on computers so that new projects could be started with the 2014 new features while allowing key projects to continue in Revit 2013. Trouble was that Revit 2014 and 2013 installed on the same computer created significant bugs in how Revit 2013 performs (notably, the ribbon needs to be refreshed between every change in command). As such, most people in our office are still running only with 2013.
Where I am headed with this is that I've heard that an install of Revit 2015 does not negatively impact other Revit software on your computer. I wondered if anybody knew this to be true and that machines with Revit 2013 and Revit 2015 installed would have no adverse work impacts to those still using Revit 2013. Anybody know?