What exactly makes you think Squeenix can make a full-fledged Final Fantasy game in only 2-3 years.
2 years isn't happening, but I don't think 3+-ish years from part 1's release is all that outlandish.
1) they've got the base gameplay figured out so they should be able to just jump into developing a bulk of the gameplay content for any subsequent releases more efficiently (they've already got a whole new playable character up & running a year after, and they had some work on Red XIII already done that they could probably use for a playable version of him), provided they don't do some kind of complete overhaul of the gameplay systems
2) there's not a whole lot they can reuse from Midgar as far as environmental assets go, but FFs generally have plenty of texture-swapped enemies & such that I'm sure they'll take advantage of that will speed up development a little bit as they can fill some of the combat with enemies that don't require a whole lot of work (different Bombs, different coloured Behemoths etc.), instead of having nothing to work with.
3) if/because it's a PS5/new-gen exclusive, that probably solves some tech bottlenecks that might've slowed down & caused issues to development otherwise (having larger traversable environments, mostly)
4) they've got the development pipeline in-house and outsourcing-wise figured out, so they can just continue taking advantage of all the partnerships with the several studios they already outsourced part 1's development to, as they are up to speed with what kind of project they are working on & SQEX has experience managing it all for a project like FFVII Remake.
5) pre-production has been confirmed to have been begun way before part 1 even released & I'd imagine much of the outline of the whole remake project was figured out during the early years of part 1's development already, so I don't think there's quite as big of a ramp-up to full production as there usually is for wholly new projects, so even if the "full production" of FFVII Remake part 2 isn't any faster than Part 1, they possibly won't have the years of pre-production to get there like with Part 1. Like take FFXVI. It started pre-production around 2015-2016 and only entered full production in, what, 2019 or something. I don't think part 2 of FFVII's remake will have such an extensive ramp-up to full production but it's more like FFXIV where they can just have a more continuous production as if they were developing expansions for an MMO rather than making a whole new game from scratch.
Or think about FFXIV. It was a hell getting out even FFXIV 1.0 and when that was a failure they were (almost) literally all hands on deck for ARR. But now? a single division of SQEX can keep pushing out a steady(ish) stream of content for the MMO every year, as well as also releasing big full expansions with significant new gameplay features & large amounts of gameplay & story content every 2 years AND develop a whole new mainline offline Final Fantasy on the side.
I think how long part 2 takes is mostly reliant on how big of a chunk they want it to advance the overarching story (and how big that even ends up being). Of course if they try to remake everything without skipping much & even trying to make it as seamless as possible (world design wise), then that might be a much longer task and... well, see you in 2026. But if they keep the scope in check, something like end of 2023 shouldn't be an impossibility.
