The 6S (see my other comment near here) was almost 30% faster than the 6, and doubled the RAM to 2GB. Those two factors alone probably made the jump seem so significant, ignoring any other changes they may have included in it. The 7 got another major clock boost, but kept the RAM (7 Plus had 3GB though) so that would've been another noticeable improvement, though mostly in games and such, many applications probably didn't see much change between the 6S and 7.