I am currently using Pro 2015 (on windows 10) but installed 2016 to check it out. A day later, I uninstalled 2016, but now none of previously created SU files (which were not even opened in 2016) are showing an icon. Upon double-clicking a blank SU file icon, it opens the Open With window and only shows 2016 as the recommended application to use to open the file. I have to right-click on any old file and choose Open with 2015in order to open it.
Any help is appreciated.