It’s about 5 times longer than previous releases were maintained for, and is an experiment. If there’s a need for a longer term support branch, there will be one. It’s pointless to start maintaining an 5+ year branch with 0 users and a handful of volunteers, none of whom are paid for doing the maintenance.
So yes, in that context, 15 months is long.
There’s plenty, but I do not wish to hijack this thread, so… have a look at the Forgejo 7.0 release notes, the PRs it links to along notable features (and a boatload of bugfixes, many of which aren’t in Gitea). Then compare when (and if) similar features or fixes were implemented in Gitea.
The major difference (apart from governance, and on a technical level) between Gitea and Forgejo is that Forgejo cherry picks from Gitea weekly (being a hard fork doesn’t mean all ties are severed, it means that development happens independently). Gitea does not cherry pick from Forgejo. They could, the license permits it, and it even permits sublicensing, so it’s not an obstacle for Gitea Cloud or Gitea EE, either. They just don’t.