From an Autodesk email:
Autodesk Revit 2015 R2 includes more than 30 user-requested features that add powerful capabilities, enhance software performance and improve user productivity for architects, MEP and structural engineers. Fully compatible with the existing Revit 2015 releases, R2 does not have a file format change and installs without disrupting ongoing work in Revit 2015.
Other key features include:
- Increased Productivity: Multiple enhancements in R2 improve modeling and work productivity
- Increased Overall Power: With new features, R2 enables you to do more
- Increased Performance: R2 meets requests for faster software performance to make work easier
You can read the announcement on In the Fold.
Read the What's New in 2015 R2 documentation.