open 2015 and verify the data. then back up the data. open 2016 and go to File > Open or Restore > Restore from Backup. select the .qbb backup file.
Resolution for '2015 to 2016 issue: 'upgrade from Quickbooks 2015 to 2016' available: Yes.
The 2015 to 2016 issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the 2015 to 2016 issue yourself by looking for a resolution described in the article. If it is a complex 2015 to 2016 issue or you are unable to solve the issue, you may contact us by clicking here or by using other 2015 to 2016 support options.
For more information about resolving issues related to 2015 to 2016 in Quickbooks/QBO or to get support for the issue 'upgrade from Quickbooks 2015 to 2016', click the link below: