[creatonez]

For the full experience:

Firefox: Press F12, go to Network, click No Throttling > change it to GPRS

Chromium: Press F12, go to Network, click No Throttling > Custom > Add Profile > Set it to 20kbps and set the profile

[extraduder_ire]

Good mention. There's probably some good art to be made by serving similar jpeg images with the speed limited server-side.