Do I need to purchase RoboSource separately?
I do believe that RoboSource is included as part of the TCS.
What folks most often grow confused about is RoboHelp Server. That one is a special and additional purchase.
Is RoboSource Control a separate component, Like RoboScreen Capture, FrameMaker in TCS 2015?
I cannot see RoboSource Control as a separate component/application in Prorams list.
RCS is a separate component that you need to install separately as well. And it has more requirements such as an MSSQL server set up to store the topics centrally. So it's more complex than simply install and use.
Check your TCS download. You should find a separate RoboHelp Source Control folder.
On another note: I would advise against using RCS. It is old, unstable and a gigantic pain to set up. If you have the possibility, I would advise to look into Microsoft Team Foundation Server (there is a free version). That one is much more stable and easier to manage and use. There is even an online version (free up to 5 people) that doesn't require you set up a server at all.