Is there a "2015" section to the Back to the Future hub?
Solution 1:
Yes, there are two Time Accelerator Switches in the 1985 Town Square, not just one.
The first, just in front of the Town Hall / Clock Tower, takes you to 1885:
The second, in front of Maxom, takes you to 2015:
The spots to return to 1985 in each case are in the equivalent location.