The route version is the lower of the two site version numbers of the route’s source and destination Replication Servers.
Replication Server version 11.5 or later uses route version information to determine which data to propagate to other sites. Information necessary for 15.0 features is not propagated to other sites until the corresponding route versions are upgraded to 1500.
After you upgrade to Replication Server 15.0 and set the site version to 1500, you must upgrade each route for which this Replication Server is a source or destination, and the site versions of the source and destination are at 1150 or higher. How you upgrade routes depends on how you use Replication Server; in particular, if you have a mixed-version replication system.
