Ok in terms of the 2 images, the 1st one is definitely more 'Real'
In terms of naturalism; I'm hinting towards agreeing with Spruce, Graffiti artists wouldn't graffiti on a wall like that, unless they just scribbled some feeble, unartistic words like: "Fugly" (not that they would use that word mind you).
Anyway, if this is for an art project, I think the first one will do, did a pretty good job of it, maybe yes make it look more grungy (if not the graffiti, then the wall, it could do with a mud-fight, looks a little pressure washed to me, but that's personal preference).
Alternatively, (Beware, longer process), open the image without the graffiti and clone-stamp, or spot heal the wall into a flat surface, dirty it up and then add the graffiti like in the first image, that's really all I can imagine you need to do to make it REAL before you go straight to real², in which case....you'd have landed yourself in a whole different dimension.
So good job, first image is a go! With minor improvements, it's as perfect as they get.