I believe the configuration for Kodi 15.2 was updated in VC 2.2.1.3.
However, if you had previously installed an older version and then updated to 2.2.1.3 your settings would not have been changed.
Try this:
1 - close VC
2 - find and delete the file .\plugins\xMySql\Options.xml
3 - restart VC, and go to xMySql settings.
4 - enter the server (if necessary), username, and password.
Try "Save and Generate" again.