Not everybody has smokin’ fast internet. Wait let me try that again. Most people don’t have smokin’ fast internet, especially not all the time. It’s part of the job to make sure our sites aren’t so slow we’re essentially depriving users access.
To experience your site with slow internet, under the Network tab of DevTools (in all browsers, you have to enable it as an experimental feature in Safari), there is a dropdown to throttle the speed. Pick one of the slower cellular speeds and give your site a whirl. Might just inspire you to find some places to speed things up.
Or, you could go to the South Pole and test. It’s not just about raw speed, it’s about latency and turbulent connections.