We upgraded to use HTTP/2 a couple years ago. One of the fringe benefits we found was being able to only send "old browser" hacks to older browsers. Nearly all of the extra libraries and things we were adding to support older browsers were not needed for anything able to connect over HTTP/2 so we don't include any of those for the upgraded connections. Additionally, we also use the push feature of HTTP/2 to initiate download of supporting assets immediately (css, images, etc) which reduces the perception of load times for end users. I can't say specifically the speed difference found when we moved to HTTP/2 as that was not the only factor involved that would impact speed results that we implemented at the same time.