Originally Posted by Michael J Fox is Canadian
There is no evidince it is not an alternate 2015 in fact the deleted scene is evidence that it IS. All that we see is hilldale.
Plus there was no mention in the movies about people suddenly gaining memories of a different timeline all of a sudden. So Marty and Doc in 2015 would still be oblivious the same way Doc was oblivious in part III when Marty comes back to 1855 to rescue him. If their memories and stuff changed, he should've already known Marty was coming to rescue him.