Lightroom 6 is a standalone version purchased as an upgrade to Lightroom 5, paid with a single upgrade fee ($79 in the US). This provided purchasers with the upgrade to Lightroom 6 and the features that were included in Lightroom 6, and entitles them to updates that provide support for new cameras that are introduced. There are no new features added to Lightroom 6. Lightroom CC 2015 is the Creative Cloud version which is actually the same program, but users subscribe and pay a monthly fee. For that monthly fee the users are entitled to new features as they are introduced, the use of Lightroom Mobile which enables them to share collections on the Web and edit them with their IOS and android mobile devices. That is the difference in a nutshell.