Hello Chad, if necessary, you can export you model back to Advance Steel 2015 by using the Advance Export option found in the "Export & Import" ribbon. This export type will create an .slmx file which is a new file type from Autodesk and will not appear as an option in 2015. However, if you edit the .smlx extension and type .gtcx you will then be able to use the file to import into Advance Steel 2015. Best Regards