What are Black's plans in this position from the Breyer defence? I'm considering taking up the Breyer defence to the Ruy Lopez as Black and played an internet game which went

  [StartPly "29"]
  [White "White"]
  [Black "Black"]
  [FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Be7 6. Re1 b5 7. Bb3 d6 8. h3 O-O 9. c3 Nb8 10. d3 Bb7 11. Nbd2 Nbd7 12. Nf1 Re8 13. Ng3 Nc5 14. Bc2 Bf8 15. Bg5


This move 15.Bg5 is not in my book on the Ruy Lopez. The computer suggests 15...h6 16.Be3 d5 which doesn't seem right unless Black gets clear compensation for the pawn. All Black's minor pieces seem well placed except the Bishop on f8. What are Black's plans in this position?
After 17 Bxc5 Bxc5 18 ed Qxd5 no pawn is lost due to the mate threat at g2.
Black has two active bishops and threatens Rad8 with pressure on the d pawn. If white does not exchange pawns then black can play Qd7 and Rad8.