2017 or 2018. It all depends on whether or not Pogba and Raiola want to allow Real a chance to garner his services, or if he's all in on a Barca move.
Not to mention the fact, Barca's wage bill is already through the roof, and will only get worse over that period. If Barca sells Neymar, that could change, but right now, they can't afford the kind of wages Pogba and Raiola would demand in order to move away from Juve. Not alongside a 120 mil transfer fee.