There's not much you can do to interrogate an R2 unit. Plus there's no guarantee that the glorified doorstop has anything of use, that's just BB8's guess. Until then, they've got the Resistance's best astromech droids and navigators doing exactly that. It'd be dangerous for them to have a copy of the map on board, considering their pursuers.

"More kids, maybe. Trained Jedi? Probably not."