I use Gmail on my 2014 Acer Chromebook C720 (2GB of RAM). Works fine. Takes a while to load initially but I leave the tab fine and it works fine for searching, reading, composing, working with labels, etc.
Weird how the web allows seemingly simple task to become so performance intensive for the computer. Reading email and performing similar tasks is nothing new to the computer world (thunderbird, outlook, evolution have worked well and fast for years).
It seems that somehow, throwing more developper at a given problem (such as email interfaces) seems to only make products slower.
Requiring 16gb or more for email is excessive.