I'm a minimalist in this regard, and I really believe that a website should only be as complex as it needs to be. If your website requires fast Internet because it's providing some really amazing service that takes advantage of those speeds, then go for it. If it's just a site to provide basic information but it loads a bunch of high-res images and videos and lengthy javascript/css files, then you should consider trimming the fat and making it smaller. Personally I always test my website on a variety of devices, including an old PC running Windows XP, a Mac from 2011 running High Sierra, an Android phone from 2016, and a Linux machine using Lynx text browser, and I test loading the site on a connection throttled to 128kbps. It doesn't have to run perfectly on all these devices, but my criterion is that it's at least usable.