If it's anything like the last ORAS demo, it's not even an actual game storyline you're playing... Just something to give you a taste. Usually they let you transfer a special Pokemon and for this demo its Ashes Greninja @(you need an account to see links)
EU got the demo hours before NA, in return NA will get the actual games DAYS before EU. Bad deal, undo pls.
I played the demo only for the transferable Ash-Greninja. It felt slightly laggy on my regular 3DSXL, I wonder if it was just my imagination or if it's a hint towards getting a "New 3DS"
Even if you play it on N3DS it still lags a bit, esp. at the trial bit where they summon Pokemon. It seems like the flames around the Dragon pokemon (forget it's name) make the frames drop too. :/ Not surprised.