- Marty: "So we go back to the future, and we stop Biff from stealing the time machine."
- Doc: "We can't, because if we travel into the future from this point in time, it will be the future of THIS reality, in which Biff is corrupt, and powerful, and married to your mother, and in which THIS has happened to ME!!"
- — Marty and Doc discussing why they cannot go back into the future of the current alternate timeline.
2015C was an ABC timeline, and was a version of 2015 created when old Biff Tannen stole the DeLorean time machine and traveled back to 1955 to give his younger self the Grays Sports Almanac, which in turn resulted in the creation of 1985A.
Marty McFly suggested to Dr. Emmett Brown in 1985A that they should travel back to 2015 and stop Biff from stealing the DeLorean in the first place. However, Doc pointed out that if they did so, it would only be the future of the current alternate timeline in which the wealthy and corrupt Biff had married Lorraine Baines McFly, having secretly murdered her husband George; and where Doc had been declared legally insane and committed to the County Asylum, as reported by the Hill Valley Telegraph of May 23, 1983.
Biff Tannen died in 1986 in this timeline, having been shot in the head by his great-grandfather Buford Tannen upon Doc Brown sending him temporarily back to 1884. Despite not existing in this timeline in 2015, the 2015B version of himself is still able to go back to 1955 and still exist there for the same reason Marty and Jennifer are able to leave 1985 to travel to a future 2015 where they still exist. The ripple effect began in 2015 and hasn't yet caught up to 1955.
Lorraine Baines McFly
In the original timeline, Lorraine Baines McFly was happily married to George McFly. In 2015C, she is a widow because both George and Biff are deceased.
Behind the scenes
- The 2015C timeline is visible in a deleted scene, with Biff being erased from existence after returning from an altered past, and the changes to the McFly home in Hilldale not visible to the viewers. The finished film only shows Biff suddenly clutching his chest in pain after he exits the DeLorean, causing the top of his cane to break off and fall inside the time machine, and staggering away before slumping to the ground behind a stationary car, where the scene ends. However, in the aforementioned deleted scene, this continued to show Biff collapsing sideways and vanishing.
- 2015C is the third version of the timeline. In the original timeline, Marty Jr. robbed the Hill Valley Payroll Substation, Marlene McFly attempted to break him out, and both were sentenced to long prison terms. In the altered version, Griff Tannen and his gang were jailed, and the McFly kids did not commit those crimes. 2015C was returned to the second version when the almanac was burned. A fourth version of the timeline was created after Marty decided not to race against Douglas J. Needles, essentially making Marty and Jennifer's future yet to be written, and as blank as the CusCo "YOU'RE FIRED!!!" fax that faded away before the latter's eyes.
- Because Biff is dead by 1986 and Lorraine uses his massive inheritance to return Hill Valley to normal, it is likely that 2015C is fairly similar to 2015B, as the city would have had twenty-nine years to rehabilitate itself and demolish the hotel casino building. As a result, it is well possible that this version of 2015 is already fully visible in Back to the Future Part II, during the scene in which Doc, Marty, Jennifer, and Einstein are traveling in the DeLorean on the skyway to depart for 1985A, by which point the ripple effect had caused Old Biff to be fully erased from existence.
- Back to the Future Part II (Deleted scene, rippling in just as Doc and Marty leave 2015, but not seen)