The TR16A sends the commands on the House Code it is set to and the unit code picked by a touchtone digit. Also on the security code, that is a three digit setting. The third digit is used for a ring indication; by sending a cycle of On Off commands to the House Code and unit code on the third security digit.
Example. House Code Dial B
Security code you key in when the beep sounds: 1-6-8
When the phone rings. It sends out a B8 On; B8 Off then B8 On; B8 Off.
I don't use the CM15A right now but if you had the TR16A send a code on B again and your modules are on C. They will not respond directly to the B signals, but a macro running in the CM15A could be triggered by the B codes to do things on the C codes.
You could also have certain modules on the B House Code and also directly control them. I use a Chime Module to sound in the cellar when the phone rings and the TR16A sends the On Off cycle. Also have an ELK doorbell detector that triggers a Powerflasher modue, to again ring my chime so to speak.