Upgrading to a new release is not something to take lightly. It is always best practice to take a non-production copy of the project and test to make sure there are no unpleasant surprises.
There is a very serious and inconvenient issue occurring increasingly often among our clients after upgrading to Revit 2015 R2. They begin seeing an error with certain families along the lines of:
“Family X is corrupt and cannot be edited. Please reload the family to repair the project” At times we have seen this problem spread throughout the project to other families causing a major headache for all involved.
The Autodesk Knowledge Network has a posted solution which states that when upgrading to R2 you should have Audit checked. That means you must take the project file in the old release and audit it when upgrading (opening using the new release). Sometimes this was done several days before noticing the issue resulting in a signficant amount of lost work!
Also remember that it is best practice to verify that everyone working on a Revit project is on the same build! With recent updates, this may be confusing, so be sure to see Revit Clinic’s post explaining what release you are on.