Note that -- at least for the trailer -- the car does have a "Mr. Fusion"™ reactor, but also has the same (or at least similar) 1985 "OUTATIME" license plate and not the 2015 barcode plate...
That's interesting, because the OUTATIME license plate never actually made any trips through the 4th dimension. It falls to the ground and spins the first time Doc sends the car 1 minute into the future during his Twin Pines Mall experiment. And the first time the barcode license plate is seen on the delorean (along with Mr Fusion) is during the end scene of BTTF1, after Doc returns from 2015 to collect Marty and Jennifer. That barcode license plate remains on the time machine until it gets destroyed by the train at the end of BTTF3.
Could it be the same car, just between the addition of the "Mr. Fusion"™ and the Hoverconversion? The need to get away from plutonium would make sense (as shown by the events ocurring in BTTF), but there's no immediate hurry to have a Hoverconversion performed on the car. No Hoverconversion means there's no need to get the DeLorean licensed to fly the skyways of Hill Valley, and thus no 2015 barcode license plate.
It's also interesting to note that in the above video, when we see a glimpse of the time circuits, the yellow one (which displays the date the car last visited) is set to XXX 00 0000 00:00 for Month, Day, Year, and Time, respectively. This might indicate that these are the Delorean's 'factory' settings and that this is the same car from
before Doc's first experiment at the Twin Pines/Lone Pine Mall.
There seem to be many contradictions which makes me think TellTale could even be adding red herring modifications to the Delorean for the trailer video clip so that nobody can guess the car's origin in advance.
On the other hand, Doc Brown, having already had the opportunity to analyze the workings of a 2015 Mr Fusion unit, could probably create his own version in 1986 to get away from nuclear reliance... or simpler still, he could have just traveled back to 2015 in his Time Train and picked up another one.
However, the problem with adding a Mr Fusion unit to the Delorean before it travels to 1955 is that when Marty arrived in 1955, he would no longer be stuck in his predicament requiring the bolt of lightning to replace plutonium. He could just toss a few food scraps into the Mr Fusion and get back to 1985 instantly. That would cause a paradox because Marty's week-long presence in 1955 was the catalyst for other time travel events and mishaps. One example, if Marty isn't in 1955 to play at the Enchantment Under the Sea dance, he won't hit the 2nd Marty in the face with the door as he exits, which is what gives Biff the opportunity to steal the Sports Almanac back. Under these circumstances, Biff wouldn't try to kill Marty with his Ford in the tunnel. This means Doc wouldn't be airborne in the Delorean at the moment when the lightning strike sends him back to 1885. We could say that, for the sake of not wanting to paradoxically interfere with the events that occurred in the films, Marty consciously uses the lightning bolt to get back to 1985, despite having Mr. Fusion attached to the Time Machine the entire time. Man, I'd really love to see a version of BTTF1 after this game takes place, just to laugh at their sense of urgency and panic of coinciding with the lightning bolt, even though the Mr Fusion is attached to the Delorean in every 1955 scene.
(Doc's probably mindful of this, though, and would likely remove the 'premature' Mr. Fusion before Marty travels back to 1955).
BTW, it really sucks that they didn't get Thomas F. Wilson to voice Biff in the game. What a shame! He does a fair amount of voice-over work these days. It would have been great if they could have gotten more of the original cast members to reprise their roles. Unfortunately, it's probably SAG's ridiculous and totalitarian union rules making it too expensive and unfeasible.