This may have been a tribute to the fact, that the year in which Marty travels to in the movie, is 2015.
The mode isn’t that good to play, in that you get 30 seconds to play, with every flux token adding up 5 additional seconds. So, it is only with careful timing and dodging of obstacles, you can get quite far. The Hill Valley 2015 background is quite neat, and a good improvement over the dull background which the game generally has.
The Hoverboard can jump to a limited height, but the car can fly to the top of the screen. You can unlock characters by collecting enough Flux tokens.
The themed content is not available in Classic Mode, but you can get it added permanently for a massive IAP bundle. The game has actually going downhill with too many In-App-Purchases for additional content which doesn’t really add much to the gameplay.
I recommend playing through the Back to the Future mode, while it is still free, and just move on to the classic mode, which I love even after three years, except for the dull graphics.