The S6 is my first AW and I think it took less than 10 minutes to do the update to 7.6 this AM.
S6 has 5Ghz WiFi, a faster chip (and perhaps also faster storage), all of which definitely help processes updates faster than previous versions, I guess the main issue is with S5 and below...
Apple could still improve the update process in other ways, but it seems S6 and beyond are already substantially better at it by pure brawl.