I have CCT 2015 (using Win7Pro64bit).
Installed both Indesign CS6 anc CC 2015 (due to old files needing CS6 release).
Default opening of .INDD file is always CS6 and if I try to open with CC it doesn't work. To open a file with CC relase I have to uninstall CS6 release.
You do it in within your operating system.
Right-click the file in Windows File Explorer
Open With >
Choose Default Program
Check "use this app for all .indd files"
Select the version of InDesign you want or browse for it
Note: I only have CC on my Mac, so I demoed this with a text file.
Note 2: Don't open the file this way as a one time thing. You are changing the defaults for all .indd files and specifying which program to use to open them. If you make a mistake, try again and keep this in mind.
On win 7 the default program is determined by the order in which they are installed, the last installed version of the program becomes the default.