Hi, been a long while since posting in the Adobe forums.
I've had the Adobe bundle since the original CS came out. Right now most of my work has been in the analog realm working in SD and I still use a number of BetacamSP decks and other VTR units.
I see that with CC2015 its easier to attain a new version of Adobe's software for generally another monthly bill. My only concern is, I still use VTR analog deck control in which CS4 was the last version to support it. I'd like to know if CC2015 can co-exist with CS4? I eventually plan to build a new workstation eventually but, the main programs I have been using was mostly PPro, Audition, PS and sometimes Acrobat. There's tons of other software in the past bundles that I would never use.
I don't care much for the cloud and prefer to have my files and everything else locally. It looks like it will be easier for me to get the newer versions of the software without the huge upfront cost that used to be from past versions.
You can have the CS4 & CC2015 together, in my personal opinion CC2015 will have advanced & new features which are not there in CS4.
From what I was told by an Adobe support person (via email) you cannot use below CS6 with CC. I would look into this further before adding CC to your computer.
They can co exist in the same computer, the applications are how much workable like will a CS4 work open in CC2015 or vice versa can not be predicted.