The code that causes it is actually in ALL versions of FfH, so it would be a good thing for other modders to comment out as well... As far as we can see, it serves absolutely no purpose. Nothing changed when removing it.
That's odd, then, that the effect would be so much more pronounced in FF and RifE. Do these two mods have vastly more promotions to cycle through, or are they stored differently? The reason I stopped playing these two mods was because of this lag, and I never noticed it in vanilla FfH or Orbis.