For Revit 2015 R2:
This update requires one of the following:
Autodesk Revit 2015 R2 for subscription customers (build: 20140905_0730)
Autodesk Revit 2015 Update Release 9 for R2 for subscription customers (build: 20150704_0715)

Link:
http://download.autodesk.com/SWDLDDLM/Updates/RVT/2015/Autodesk_Revit_2015-x64_Update10_forR2.exe   

Readme:
Autodesk Revit 2015 Update Release 10 for R2 Readme

Enhancements (not live yet):
http://revit.downloads.autodesk.com/download/2015RVT_RTM/UR10/Enhancements_List_RVT_2015_UR10_forR2.pdf

Additional links will be added as they become available…