If you own the FFG Star Wars books, do you need the Genesys Core Book to start playing it?

As a long time player of the FFG Star Wars games (Edge of the Empire, Age of Rebellion, and Force and Destiny), I was very excited to hear about the release of FFG’s new RPG Genesys, which uses the same Narrative Dice System (albeit with slightly altered dice). While I was pleased to hear about it’s release, I was wondering if the $ 40 price tag was worth it if I already had all of the Star Wars RPG core books.

Are the rules exactly the same (obviously with altered classes, races, etc.), or is it changed enough to warrant purchasing the new book? Is it possible to play in non–Star Wars worlds with the Star Wars books?

Ultimately, what I’m asking is whether it’s different enough to require buying the new book to “play Genesys”, or whether I can “play Genesys” using the rules in my Star Wars RPG books.