I like Revenge of the Sith, so I’d say if somebody is interested in Star Wars, might as well give that movie a try. But in general I don’t think you “need” to see it to appreciate Episode VII.
That said, what rock have people been living under to not have seen the Star Wars trilogy? 😄
As for a hypothetical order for somebody who has never seen Star Wars? I’d say marathon the original trilogy (preferably before they started messing with it, or the Despecialized version). And then if they’re hungry for more, throw on Revenge of the Sith for a one-off tale of weird darkness. And of course see The Force Awakens.