If you already have VS2015, then you need to install the Pega Robotics Studio Plugin. I do not know where you are seeing the reference to Office in the title of the installers as that is not something Pega includes in the title. One of the options when installing Studio, the Plugin, or Runtime is to select the Office version to allow your solutions to integrate with MS Office, however there is no separate installer for each supported Office version.
Ok thanks all. If I'm interpreting this information right, it sounds like if I have VS2015, I only need Pega Robotics Studio Plugin, and that's it for both development and testing. If I want to just run (load the automation) what I built afterward from the perspective of a user, I'm guessing that only the Plugin is still only what I need.
No, plugin is used to develop automations and without plugin also you can develop automation (but in this you don't have full visual studio). If you install pega robotics studio then it will install visual studio shell. Plugin will be installed on top of visual studio.
To run or load automation in user's machine (I mean in production environment) you have to use Pega Robotics Runtime only.