I would suggest trying "Sign In with a different Quicken ID" and signing in with your current Quicken ID/password.
Did you copy the QUICKEN.INI file in C:\ProgramData\Intuit\Quicken\Config\ from the other computer? If that doesn't work, you can try the whole Config folder.
See:
The only thing I can suggest is uninstalling Quicken 2015, reinstalling with the internet disabled, install the R17.4 Mondo patch, replace the Config folder and then running Quicken.