hc,
We have this configuration CC/CC 2014 running in one of our all-Mac computer labs without any issues. We have some faculty running both on their Windows workstations. However, doing this is not a standard practice here. Have you been able to poke into any system/installer logs to get a fine-grained look at where the errors are happening?
I know this isn't very helpful, but it's my understanding that part of the reason Adobe went this route rather than making 2014 an update is that so commercial shops can run both in parallel and move when they're ready. This has been something of a nightmare for us, because most classrooms, labs, curricula and textbooks are on the original CC and our students are all using CC 2014. (Sorry, had to vent a bit.)
Ric