Yes, basically just a few years. Sauron was defeated twice in the Second Age - once by the Elves and Numenoreans soon after forging the rings and then again at the very end by Isildur. These two events are ~1500 years apart as you have said.
But they already have mentioned that Sauron had been defeated, but not elminated and Galadriel was scouring ME for any evidendence of his return. So they are moving the forging of the rings until after the first defeat.
I wouldn't call if fan-fic, which is to me either filling in gaps through side-stories, prequels and sequels that don't conflict with anything in canon. Like let's say you had a little side story about what Luke Skywalker did on Tatooine before meeting Obi Wan Kenobi., or something in between ROTJ and TFA - like what they're doing with The Mandalorian and baby Yoda. Its not even a retcon, which is still a somewhat plausible reinterpretation of past events.
What they're doing is is actively contradicting canon. Basically rewriting.