Hi Robert,
I noticed that your forum post have not been answered yet.
Do you still have problems loading your model?
From your issue description I am not sure if I have understood you correctly, especially I don't understand why you need a subscription account.
It is possible to download a trial version of InfraWorks 360. During the installation you will get a temporary Autodesk 360 account that enables you to work and collaborate in the cloud. This account will be disabled approximately 30 days after your trial version expired.
If you need to upgrade the program, i.e. from InfraWorks 360 2015.2 to 2015.3, simply download and install the trial version again - uninstallation of 2015.2 before might be needed.
Regards,
Karsten.