In the original trilogy, everybody knows about The Force, whether they believe it, or not ... despite the fact that there have been no Jedi for decades. Now, though, if the previews are anything to go by, nobody knows what The Force is, or who the Jedi are/were. It's nothing, really, but I don't know ... it just seems kind of silly to me.
But look at it from another
point of view... (ha! I done did a reference)
Episodes 1, 2 and 3 take place over a period of about 25 years... and Ep3 is set about 20 years before Ep4... in Ep4 the Jedi are long gone after the events of EP3, with only Obi and Yoda left. And both were basically in hiding.
Vader was doing his thing, and was called a relic of an extinct religion by one of his own men.
Then, by the end of Episode 6, there was only Luke left out of the actual Jedi... he then contributed toward the extinction on the Sith with the deaths of Vader and Palpatine... even Yoda said "The last of the Jedi, will you be"...
Luke is the only one left. No other Force users existed at the end of Ep6.
Then, another 30 years later we get Ep7 and from Episode 1 to Episode 6, there's a span of about 60 years.
Ep7 is close to 100 years after Episode 1.
Also, "We've heard stories about what happened" and Han replies with "It's true, all of it. The Dark Side, the Jedi... they're real"
What we don't know is if Han is referring to "The Jedi", meaning the Order,
them... or if he's saying "The Jedi" meaning
Luke Skywalker.
In real life terms, with the timelines that have passed, the stories they've all heard are like people today talking about something that happened in the late 1800s and early 1900s.
It seems that what happened in Eps 1-6 are legends and myths in Ep 7.
Also, the Galaxy is a big place... so it's no wonder these stories aren't super-common knowledge amongst absolutely everyone everywhere...
... also Rey is from a planet called Jakku, that as far as I can tell was never part of the Empire, or the Republic for that matter... so it's no wonder the stories she's heard about something that happened a century ago on the other side of the Galaxy are kinda mythological.