Before the NFS 2015 was released, we were informed that the game would require constant internet connection. However, Marcus Nilsson stated in September 2015 that the game might eventually get an offline mode in a patch, because he wanted the people to play it even after the servers were closed. Here's the proof: http://racinggamemania.com/need-for-speed/need-for-speed-offline-mode-may-come-in-a-patch/
I know the "living game" has barely been released, but it seems it's dying already (no new content coming). The "living game" thing was also the official reason why the game required internet connection, so there's no excuse for having this requirement anymore.
So I'd like to ask a simple question. Is the offline mode still coming, Mr Nilsson? Will we be able to play NFS2015 in 10, 20 or 30 years from now?