Lightroom CC 2014 (aka Lightroom 5) cannot read newer Lightroom CC 2015 (aka Lightroom 6) catalogs – they can't go backwards, sorry about that...
You can go the other way with catalogs however, if that helps at all.
You can try to use xmp sidecar files with your raw files or dng files instead of a catalog to transfer files and settings. Most of the settings done in 2015 Develop should translate into 2014
Prodesign and Jao
So now I have LR cc, LR cc 2014 (5) and LR cc 2015 (6) and they are not compatible.
Does that mean that I will need to keep the old versions and remember which catalogs are for which version?
Some of the extension tools that were made for LR cc (watercolor assistant for example) cannot be used with the new versions.
The old catalogs will open and convert in the new one but the simplest way to work is to go to the new version completely and only use a single catalog.
I have never heard of watercolor assistant for Lightroom. Is that a Photoshop extension instead of a Lightroom one? Most of the time it is just a question of time before plugin manufacturers update their plugins.
I am sorry the water color assistant is a plugin for PS CC not light room.
When they upgraded the PS from CC to CC 2014, it stopped working (since it was developed for the CC and PS CS6. - https://creative.adobe.com/addons/products/1652#.VU-iEZOMYZw
I am working with one large catalog, but in the college they have not updated the LR to the newest version. Which means that I need to export all my images to be able to see them in Bridge. It is becoming complicated, instead of easier.
If you are using Bridge, you shouldn't need to export. You can just write metadata to all your files and all edits should be visible in Bridge and camera raw when you browse to your images except perhaps for those edits that are not possible in the previous camera raw.