We had everyone on the Realm at the max render distance. As shown in the attached video, `high-render-lag.mp4`, the phantom was incredibly slow.

Edit 1: Being on mobile, I already knew how long it approximately takes for my device to load up after switching dimensions. With everyone at the game's maximum if provides normally on our sliders, the dimension time to load, and even just to switch to the game's loading screen for it, was significantly longer. /Edit1

Aside: If possible, can someone forward this so an official "Minecraft news" segment talk about why having a high render distance affects everyone who want to enjoy the game, and thus is bad for fair gameplay?