The Doc in 1985 was around 60 years old and would've been 90 in 2015. It's highly unlikely that the Doc who came back for Marty is the a naturally aged (and de-aged with surgery) Doc native to 2015. And we do know where the Doc at the end of BttF is going he out-right tells Marty he's going thirty years into the future.
I believe you misunderstood his point. I believe he meant that the Doc who traveled 30 years into the future then spent around 20 years (Doc's personal time/age) time traveling after that. Where he could see that that one mistake of Marty Jr.'s led the McFly family down the path of ruin (remember the newspaper that changed was from a few days father ahead from where Doc took Marty to fix it). He even says he traveled further ahead to see what happens. This is why he needed the rejuvenation surgery to make himself appear the same age as when he left 1985 and be recognizable to Marty. So it is obvious that he did more than a single jump forward and then back to 1985, even though he was only gone a couple of hours in real time.
So the Doc Brown that came back to get Marty in 1985 was quite possibly only one of an infinite potential of alternate time-line Doc's. In fact, the original Doc Brown from BTTF1 died! When Marty returned to 1985 at the end of the movie, he returned to an alternate time line. One where George McFly became an author, the Twin Pine Mall became the Lone Pine Mall, and Doc learned the fate of the original and took steps to avoid the fatality. But in that original time line, which actually still exists but is no longer the powered up Prime Reality, Marty disappeared forever that night, Doc Brown was found dead in the Twin Pine Mall parking lot, and the Libyans likely got away after their VW bus crashed into the Photomat.