There is a small change on the Revit 2015 SDK regarding the Add-In Manager: it now comes with just the .dll and .addin files, we removed the MSI installer.
Important: make sure you download the latest release of the SDK from the Developer Center (later than May 14, 2014).
Here are the steps to use it:
- Copy the .dll and .addin files from the Revit SDK folder (\Revit 2015 SDK\Add-In Manager\) file to Revit Addin folder (i.e. C:\Users\ <<USERNAME>>\AppData\Roaming\Autodesk\Revit\Addins\2015\).
- Adjust the <Assembly> attribute to the correct path, or leave just file name.
- Inside Revit, it should appear at the Addins tab under External Tools menu, as shown below.