2015 feels like a half completed game, the basics are solid though, but with 2016 looking really good, I would say go for that.
The issue with any Codemasters F1 game so far has been the plethora of bugs after release. So let's be cautiously optimistic and wait for some reviews and patches.
Aside from that, from the videos and info I've seen so far, feature-wise it might be the most "complete" F1 game to date (though I'm not too knowledgeable on the various console-only F1 games before Codemasters took over).
From SC/VSC over formation lap to full player-character career with R&D... the F1 feeling is there. They even seem to pay big attention to tyre wear/strategy and giving the player more info to make the right decisions.