Blocs makes this pretty easy, by simply selecting the lazy loading option when exporting the project. The images only load at that point as the page scrolls down, which makes the initial page load very fast. You can also tick the various other optimisation options when exporting the project.
Apart from that you can make all sorts of changes at the server level, depending on what your hosting package allows or consider options like CloudFlare.
I always choose the Export Project option, which allows me to select the export settings, but I have no idea what is done if you simply select Quick Export.