Studio 2015 doesn't recognize wsxz packages

Yesterday I finally installed Studio 2015 and it seems it has problems with packages in wsxz format. This format doesn't show on a list of supported files. When trying to open the package via double click I get the following error: https://dl.dropboxusercontent.com/u/87169/screen.png
How can I fix this problem? Right now I have to open packages in Studio 2014 and then move projects to Studio 2015.