Depending which Revit 2015 installer you used, you may need to install this. More info at:
http://download.autodesk.com/SWDLDDLM/Updates/2015/REVIT/Revit_2015_Update_1_Readme.htm
Revit 2015 Update Release 1 Enhancements documentation:
http://revit.downloads.autodesk.com/download/2015RVT_RTM/UR1/Enhancements_List_RVT_2015_UR1.pdf
Autodesk® Revit® Platform 2015 Enhancements
- Improves data integrity when editing nested families.
- Improves stability when editing nested families.
- Improves stability when editing when expanding schedule columns.
- Improves upgrade of projects which contain rebar elements.
- Removes format constraints for assembly codes.
- Improves data collection when Customer Involvement Program is enabled
Just remember – the application manager will by default store downloaded packages in:
C:UsersUSERNAMEDocumentsAutodesk Application Manager