This is confusing! I installed Update Release 3 when it came out in June, and now (as of 9/17) they've come out with Release 2? And get this: "This update requires either the initial release of Autodesk Revit 2015 (build: 20140223_1515) or Autodesk Revit 2015 Update Release 3 (build: 20140606_1530) . Autodesk Revit 2015 Update Release 3 will need to be applied to any installed Revit 2015 which has either Autodesk Revit 2015 Update Release 1 (build: 20140322_1515) or Autodesk Revit 2015 Update Release 2 (build: 20140323_1530) applied. Installation will also be blocked if Autodesk Revit 2015 Update Release 4 (build: 20140903_1530)) has been applied, a full uninstall followed by a new install of Autodesk Revit 2015 will be needed in order to apply Release 2." Sheesh!