the memory issue exacerbates it I bet, but hangouts takes a long time to load no matter the phone I believe (at least 'first load'). It should be quick after it is cached in ram though
Switching to it is slow as heck, too. For example, when tapping a Hangouts notification on the lock screen, then finger print unlocking so that it loads directly into the message in Hangouts takes forever.
Likewise, tapping on the Hangouts notification from the pull down menu to switch to it also takes forever.
Forever = a solid second or sometimes even two.
It's annoying.