It's been problematic in Germany for a long while. But it was dependent on the ISP in use. German Telekom has (or had?) massive bandwidth problems in high traffic times (i.e. evenings and weekends), making even 360P videos unplayable with a good connection. Other providers I used (Alice for while) never had these problems. One way to circumvent this was to use a different proxy or VPN... but that's not really an option.
Youtube has this page, which shows your ISPs connection speed and others... maybe it shows congestion, too
And by congestion, I mean "the ISP doesn't buy enough bandwidth", not that the "internet is full". Decix (Europes connection to the US) is still at only 10% PEAK!