Set AutoCAD 2015 as default for opening a DWG by dbl clicking the file

I'm stumped. I have multiple versions of AutoCAD on my machine. No matter what I do when I dbl click on a DWG file it opens in R2014. I want it to open in R2015.

So I "right clicked", chose "open with" / "choose default" and went to the R2015 folder and clicked ACAD.exe, it opened in R2011!

It then goes back to opening in R2014 the next time I dbl click.

There has to be a way around this. In the registry maybe?

Help!