Evaluating and plans in a Nimzo-Indian position

Hi, seeking some pointers in evaluating (from Black's perspective) the below position that was reached in a Nimzo-Indian:



Qn 1: how do we evaluate this position? White's connected pawns in the centre looks quite menacing, but engine evaluates Black with an advantage (-2.x)

Qn 2: Engine suggests just trading 15. ...Nxe4 16. Qxe4—in this line, what would Black's plans be? ...Rac8 preparing ...c5?

I played 15. ...Nd5 trying to attack White's e3 pawn but of course White just defended. I also missed 17. c5 which gave the knight the boot.

Thank you.

I haven't read the comments but I was thinking: what? why not swapping the Knights being a pawn up? Maybe followed by Qd5.