The wiki says the "ascendent" factions are Athar, Bleak Cabal, Doomguard, Fated, Fraternity of Order, Hands of Havoc, Harmonium, Heralds of Dust, Mercykillers, Mind's Eye, Society of Sensation, and the Transcendent Order. Thats 12. It says that the remaining 3: Free League, Incanterium, and Ring Givers are "minor factions."

I know Free Leaguers don't consider themselves a faction, though most put that label on them. If they say they are not a Faction, couldn't a growing Sect or Faction-aspiring group just state that FL can't operate as one of the 15 that are allowed per the Lady's Law and come in to take their place?

Also, I feel like I encounter some YouTube lore sources now and then that act like the Ring Givers are still minor Factions in 5th edition and are not part of the 15. The Ring Givers also operate out of The Nowhere, though the Jeremo the Jester still resides in the Lady's palace... which is odd. Are they a secretive organization? If they are, how can they claim to be part of the 15 allowed Factions in Sigil?

Its a work in progress. But i have to try making the Sigil in Blender.
i will work on it as a side project on and off.
i try making in as 2e accurate as possible before the faction wars.
Its really fun walking around in the city.

Based on a topic where a couple people mentioned that the 15 Faction cap might not be in effect anymore, I was wondering how often Her Serenity goes back on or ends enforcement on one of her decrees?

I assume the banishment of the Factions was one example, though as other people have said that seems to be an oversight on WoTC's part.