Images shouldn't be loaded until they need to be shown (say if they're below the fold). Additionally, the page waits for the gr-avatar images to be loaded before the onload event is fired. The images loaded only have a cache-control max-age of one day.
Given the number of avatar images (should the instance be configured to show them) on each page load, this could be an easily-implemented solution with a win on the page Load metric:
+ Don't block the page load event on gr-avatar images.
+ Lazy-load based on visibility.