Premiere Elements 12 Mac does not include Mac 10.11 El Captain in its System Requirements. One reason, 10.11 was not around when 12 was released. Consequently, I seem to be seeing reports that Premiere Elements 12 Mac is not supported by 10.11 seemingly based on the condition that Adobe has not tested it. This seems to be the case for 13/13.1 and 14 as well. Yet users are reporting 13/13.1 Mac and 14 Mac working on 10.11 while others have problems.
How easy would it be for you to upgrade to 10.11 and determine first hand if Premiere Elements 12/12.1 Mac is going to work for you on your specific 10.11 computer environment?
I am not sure what type of a safety net you would have if someone told you that yes Premiere Elements 12 Mac" works on Mac 10.11 El Capitan.
Please update us on your progress as your schedule permits.