Update (November 2016): It looks like the C # Interactive tool window has been re-entered. I am using VS 2015 Update 3, which has it; but it may have been reintroduced in VS 2015 Update 1 already.
You missed the fact that the blog articles you link to were published back in 2011, where VS 2015 was not yet on the horizon. These articles apply to VS 2010 and (I assume) a very early version of Roslyn.
By the way, CTP is a preliminary version of the product. As long as Microsoft is at the CTP stage, it is subject to the possibility of rapid and even short-term performance changes. Therefore, even if these articles are applicable to VS 2015, they should be about the same version of the product that you are using; otherwise, you would not be guaranteed that they contain updated information.
See also:
stakx
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