Fifteen million merits is maybe the
least about the future of any Black Mirror episode. It reads best as entirely a comment on the society we already have.
A big clue is that the world in it doesn’t make a ton of internal sense and the episode makes absolutely no effort to smooth that over. The questions it raises and leaves open without even attempting an answer are on purpose. You’re supposed to go “god, bicycling to make little pellets? Just to buy useless trash? God, why? It’s so pointless,” or, “they truly look down on and are mean to the people who get demoted, even though they’re basically guaranteed to end up that way someday, when their health or good fortune run out? Just cruelty for no reason that’s highly likely to hit them some day, too? That’s insane!”
… because actually it’s about now (or, the year it came out) and the point is to get you to connect the dots and realize we’re doing the same crap and just don’t notice. It’s only “sci fi” as some sleight of hand to give you an alien’s eye view of our own actual society as a way to prompt reflection. The core story of the corruption of a “revolutionary” to serve the purposes of the system is some bog-standard media studies stuff pertaining to today, not sci fi. The reveal that they could just fucking stop all this and go outside, it’s not some alien world or a post apocalypse after all is yet another thing that’s supposed to make you go “what’s wrong with them? Oh. Right. It’s us.”[1]
Long winded way to say: we can’t “end up” at Fifteen Million Merits future-world, because it’s just our own world we’re already in.
[1] Some read the final scene as depicting yet another viewscreen, but this is such a wildly weaker reading as far as the how effective the scene is that I can’t believe it’s intended that way.