When remaining still (so as to not load chunks) network usage is abnormally higher in overworld in comparison to the Nether. I notice an average of 300-400 KB/s network activity when in overworld.

I attached 2 screenshots from minecraft:

Nether Rx: 510

Overworld Rx: 5930

I also attached screenshot from system monitor where you can compare network usage when switching dimensions from nether portal and waiting some time. There is an initial expected increased activity (probably for chunk loading) but after that overworld's usage is much higher.

Client: Linux 5.8.0-48-generic Ubuntu 20.10 java version "13.0.2" (Oracle not openJDK)

Server: Linux 5.4.0-70-generic Ubuntu 20.04.2 java version "15.0.2" (Orance not OpenJDK)