That report, which Leonov was a co-author of, identified the other plane as a MiG-21, not a Su-15, but otherwise seems pretty similar to this account.
I'm not sure why RT here is reporting Leonov's updated version of events as if it were just now made public, either. He published this version (involving the low-flying Su-15 passing within 10-20 meters) at least as early as 2004, since it appears in English in his co-written book Two Sides of the Moon (http://www.amazon.com/gp/product/0312308663/ref=as_li_ss_tl?... ; Chapter 8).
The story itself is covered widely by Russian media so while you're right about RT in general, in this particular case, the RT thing is incidental.
Every time I turn it on, though, they seem to either be slating the United States or peddling conspiracy theories off the internet. It's strange. I'd watch it if they talked about their own country.
http://www.amazon.co.uk/Starman-Truth-Behind-Legend-Gagarin/...