I figure if I can accept the fact that Anakin built C-3P0 on Tatooine, ending with 3P0 being bought by the Lars family in Attack of the Clones and ending up back there with R2 in A New Hope conviniently in the company of Luke, Anakin's son, to come across Obi-Wan and regrouping with Leia, Luke's sister, on the Death Star with Vader waddling around - I think I can accept that R2 wakes up from BB8 speaking with him about the map.
Maybe it could have been executed better, but it's fine as is. It's not like R2 had a secondary piece of the map. He had what I assume was the map of the entire Galaxy, minus a fairly large portion. It would be nice to know where that piece went and who took it out though. Unless it was removed and hidden by the Jedi after the rise of the Empire. Then our friend on Jakku finds it and contacts the Resistance.

On a side note I think I'm going loopy. I've become so used to CGI, and finding it extremely frustrating to see in films, that I swear I'm seeing CGI in this where there is none - like h hanger as Poe and Finn get to the fighters. I know some of it will be CGI, but it's just the way the lighting is. Some of he lighting in this film is gorgeous, and I know I'm seeing real sets, but after so much CG, my mind is struggling to grasp it now.