I am considering going from LR 5 to CC2015, what happens to my installed version of 5, particularly if I decide i don't like the subscription service
Lightroom 5 remains installed, intact, and completely usable as a separate program. The installation of Lightroom CC will see your Lightroom 5 catalog and prompt you to upgrade it. That process will create a complete new copy of your catalog that is compatible with Lightroom CC. The Lightroom 5 catalog is left in its current state. Just remember that any work that you do in Lightroom CC using the new catalog cannot be accessed using Lightroom 5. However, those images that might be new to Lightroom CC can be imported into your Lightroom 5 catalog, and you can start over.
Thank you very much.