There have been numerous reports of SL databases not showing up after an upgrade to SL 2015. Once the upgrade scenario is run, the databases do not appear in the “Find Databases” window.
The cause of the databases not showing up after an upgrade to SL 2015 is because of the Trustworthy property on the Database being set to False. To resolve the issue, log into Microsoft SQL Server Management Studio, right-click on the database that is not showing, and choose Properties. In the Properties window, locate the Trustworthy property and change it from False to True.