You're assuming they're recommending the movies to see based on someone having limited time.
If someone asks me which movies they should see before this, I'm gonna recommend everything but Incredible Hulk, Iron Man 3, Ant-Man, and Homecoming. If they say time is of the essence, I'd add Black Panther, Thor 1, and Iron Man 2 to the discarded pile.
I think enough development of the Guardians dynamics happens in Guardians 2 to recommend someone watch that first, especially since Mantis proves pretty useful at one point, and Groot immediately being a teenager if you only saw him in Guardians 1 might be weird.