I can't tell if the thread has some sort of running gag or if you're actually confused by the concept.
You don't have to make the future 2015. You don't have to make the past 1955. You're making the film, today, not when it was actually made, thats the entire point of the prompt.
I feel like the future being 2055 is extremely in line with the gag. Because we make the movie in 2025. And the plot is going 30 years into the future.
You just have to switch the first and second future, the default future is the Biff timeline, then you have to change the future to make the hoverboard timeline.
That would actually be so cool but I can already see the scathing online criticisms:
"New WOKE BTTF2 ruins a family movie with vulgar dystopian future, not an ounce of original thinking in the writer's room. Entire second act of film missing as plot is resolved in only 1 trip."
Might be better to just stick to original stories and concepts, tbh.