I just checked uMatrix how many scripts are running. After blocking hangouts, plus, play, notifications and whatever "ogs" stands for it got a bit snappier, and it still works.
In this case I had it set up to allow all subdomains of google, so I opened the panel and clicked to blacklist the subdomain that I didn't want.
EDIT: The only downside of this is that if I want to use Google Hangouts in the same browser, it is now blocked, so I have to manually unblock it. But I use Firefox as my main browser, yet reserve hangouts to Chromium anyway.
Haven't used it extensively, but blocking the following domains sped things up a little:
- hangouts.google.com - plus.google.com - play.google.com