I have a Moto G5+ with 2GB of ram. Switfkey generally occupies <50MB, but after a few days of use it will hold onto at least 150MB+. Even switching to another keyboard and verifying that Switfkey is not resident in ram and leaving it off for a day, it will grab 150MB+ again when re-enabled. Only a reboot will bring it back down to >50MB which will then stay that way for a few days. Also when looking at Swiftkeys history, it will grab up to 500MB of ram. Why does a keyboard need that much? BTW, I have cleared it cache etc.
I know some will suggest, this in not a big deal, as Android deals with ram pretty well. But I start to notice apps I use regularly starting to reload again because Android is taking back the ram to use elsewhere. When I kill Swiftkey, things run smooth again.