To reduce contention and improve performance, the default locking schema for the system tables in the Replication Server System Database (RSSD) is row-level locking when you install or upgrade to version 15.5.
The locking schema does not change when you downgrade from version 15.5.
There is no change in the default locking schema for the Embedded Replication Server System Database (ERSSD), which is row-level locking.