I am a current Lightroom 5.7 user - I have purchased and installed Lightroom 6, but have not launched the program yet - will LR 6 make changes to my LR 5 catalog, such that it cannot be used in LR5?
Also, can LR6 and LR CC 2015 share the same catalog?
Lightroom 6 will require an updated database are catalog format. When you first start Lightroom 6 after you have installed it, it will prompt you to upgrade your catalog. This will create a new copy of your catalog in the new format, leaving your Lightroom 5 catalog intact and usable if you still have Lightroom 5 installed. Lightroom 6 and Lightroom CC can use the same catalog. But they cannot share the same catalog because that catalog must be installed locally on both computers. The Lightroom catalog cannot be placed on a network drive.