Move our younger one to her sister's school for LKG, or keep her at the preschool she loves?

Our little one is finishing nursery at a small preschool near us in Madhapur. She is very happy there, knows every aunty by name, and they run up to UKG. Her older sister is at an ICSE school about twenty minutes away, and that school has an LKG section with a sibling seat available if we confirm this month. The practical case is easy: one drop, one calendar, one set of holidays. My partner is home right now on a career break, so the double drop isn't a crisis this year, but it won't always be like that. The other case is that she is barely four and thriving where she is, and the big school feels big. For those who moved a younger child early to be with a sibling, or waited until class 1, how did it go? I'm leaning one way on Monday and the other way by Wednesday.