I had a FMS 14 running under MacOs Sierra.
I stop FMS 14 with the console and copy my files.fmp12 on the desktop.
I uninstalled FMS14 and installed FMS 15 Trial.
When installation done I get the message which ask me if I want to continue to start the Deployment assistant.
I click continue.
After 1 minute Safari shows me the following message:
The Database Server is not available. To edit server deployment, please start the Database Server first.
When I try to launch the console (http://localhost:16001/admin-console/) of course it does not work -> normal.
I try on a old Macintosh available running El Captain and I get exactly the same issue.
Same problem after restart.
The purpose is to try FMS15 before buying the update from FMS14.