the new version of langprefix
I doubt that.
I could well imagine that [[water]] is made faster by micro-optimizations like this, but it's not representative, and we shouldn't make Wiktionary-wide design decisions based on it.
(If need be, we can just take a DUDES ALREADY KNOW ABOUT CHICKENS approach to that entry.)
The alternative would be specifying sc=Latn over and over on large pages. (Yes, this actually reduces server load considerably!) I don't think that is what you want, is it?