Ok, sometimes your Autodesk software keeps failing on the activation process, generating an 0015.111 error.
This happens when, in the installation process, you choose to include the product Service Pack, when available. So, the first step is not to select this option when you install the software.
But if you missed this issue, now you can follow this procedure to bypass the problem.
1. Open Task Manager> Processes and kill all Autodesk running processes;
2. Go to the installer folder (if you didn't delete it yet), and find the following folders (use the adequate for the version of your software):
C:\Autodesk\<your product>\x64\RVT2015\Program Files\<your product>Common Files (64-bit)|Autodesk Shared\AdLM\R9
3. Copy this two files adlmact.dll & adlmact_libFNP.dll to the folder:
C:\Program Files\Common Files\Autodesk Shared\AdLM\R7 for release 2014
C:\Program Files\Common Files\Autodesk Shared\AdLM\R9 for release 2015
C:\Program Files\Common Files\Autodesk Shared\AdLM\R11 for release 2016
Now you can try to activate again.