Replication Server 15.0.1 has a new configuration parameter, stats_reset_rssd, which allows you to optionally keep the old sampling data in the Replication Server System Database (RSSD) by setting its value to off. By default, stats_reset_rssd is turned on.
configure replication server
set stats_reset_rssd to {"on", "off"}
See Chapter 3, “Replication Server Commands” of the Replication Server Reference Manual, for detailed information about the admin stats command.