Basically, what these replies are telling you is that what you were told is wrong. Or at least misinterpreted.
Selecting E only will not increase queue speeds, but limit them.

Logically speaking, if you're playing on an English data centre and only select J, you probably won't be seeing speedy results. So if someone told you "Hey Kat, you've got J selected. You should select E if you want faster queues!" this isn't them saying E only. If anyone actually told you this is up to my imagination as I'm sure I'll never know for sure!