Upgrade from 4.7.14 to 4.7.15 failed on Database Upgrade
I experienced this same error today.  In my case, I had mistyped a command into the version control system - so I had a Civi 4.7.15 database with a Civi 4.4 file system!

In Civi 4.7, the way that configurations were stored in Civi changed.  You would only get this error if the code that was running was old.  I would check to see if you have another copy of CiviCRM somewhere in your filesystem.  Feel free to comment on my answer if you'd like some followup on how to find what I'm describing; let me know how you access your filesystem.