One of the big features brought to Version 15.0 is the ability to do an Active Upgrade - an upgrade of the MUF while it is currently running. This is available to our clients who are running Version 14.0, and is a significant change from upgrades for previous versions. This is why that process is featured in the documentation.
However, the same process used in previous versions is also still available. In the documentation for CA Datacom/AD Version 15.0, there is a section called Starting Your Product that will help you with this. We will assume that you have created your SMP/E environment already - either using CA Chorus Software Manager (called CSM, formerly CA Mainframe Software Manager, or MSM), or by manually running the Installation jobs.
In this Starting Your Product section, you will learn that you should be sure to use a unique name for your CXX/MUF, and that the best practices indicate that the CXX/MUF name should be no more than seven characters (especially if you use a Shadow MUF).
In this section is also the Installation Sequence to use and the Customization and Environment Steps to follow to create your new Version 15.0 MUF. This new MUF will be completely separate from your current 12.0 MUF, and will have all new operational, control and database files. Once the installation is done, you will skip over to the section Migrating/Porting Phase for Non-SQL Created Databases, and this will tell you about the AXPOR01 job to move your current base application database files from the "old" MUF to the "new" MUF, which will complete the upgrade. Both "old" and "new" MUFs will need to be running concurrently for this job.
Until you run this last AXPOR01 job, your current system is not affected, as all the other jobs will be run to create the "new" MUF. Then, when you are ready to complete the upgrade, you will need to shut down your applications that use this MUF, run the AXPOR01 job, update your JCL for the application to reference the new Version 15.0 loadlibs, and then you can start your application to run against the version 15.0 MUF.