Can a human very easily hear the difference in sound between FLAC and Spotify’s “very high” quality streaming?

No!

The average human can’t really tell the difference between the sound quality. There are always going to be people who think they can easily tell the difference, but when this is put to the test it is very difficult (especially if you don’t have the best listening equipment).

It’s obvious that the better the listening equipment the more likely you are to hear the differences. However, the average consumer simply can’t afford a $1000 speaker or more.