The Backup Exec Device and Media Service cannot start because it detected a database schema version mismatch

I have one CAS with BE2014 and MS SQL Server 2008 SP3 installed, one  MMS with BE2014 and MS SQL server 2008 R2 (combined in BE2014 package)

I removed BE2014 and MS SQL Server 2008 SP3 and then reinstalled my CAS with BE2015 and MS SQL Server 2008 SP3. Keep MMS unchanged.

After that , I found the Backup Exec Device and Media Service cannot start with error

"The Backup Exec Device and Media Service cannot start because it detected a database schema version mismatch"

Can you advise if schema version mismatch is due to the DB version I installed on MMS is of MS SQL Server 2008 R2, but the DB on CAS is MS SQL server 2008 SP3?

Or It is because DB schema different in BE2015 and BE2014? Not related to the DB version on CAS and MMS ? Thanks