The list of the enhancements in MSR 3.1.5 includes:

Introduction of the apply command

The new apply command takes the place of the scale, upgrade, and install commands. The msr-installer now determines which operation to perform based on the configuration specified in the values.yml file.

MSR can now be configured with an even number of replicas

Users can now use the --force flag to configure an MSR deployment with an even number of replicas, and thus override the recommendation check in the apply command. Be advised that Mirantis does not recommend running an even number of replicas in a production environment.