Well I mean this doesn't seem unreasonable as you picked the 3rd most common reponse to the exchange variation in 9. nbd7 then he followed it up with a vary rare response instead of 10. 0-0-0 he played Rd1 which is seen much less.  Then after white's 13th move I already can only find one game in this position so it's no so surprising that you reached a new move on move 15.  As for this line, I don't trust it at all.  Both c6 and Re8 are theoretically much stronger and the passive play required by this line doesn't exaclty make it all that appealing, I think in the line you gave white already has somewhere between a slight advantage and a clear advantage.

Hi,

Recently I faced a (at least for me) TN in the Exchange KID. After 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 0-0 6.Be2 e5 7.dxe5 dxe5 8.Qxd8 Rxd8 9.Bg5 Nbd7 10.Rd1 Rf8 11.Nd5 c6 12.Ne7+ Kh8 13.Be3 Re8 14.Nxc8 Raxc8, my opponent played 15.g4!? simply threatening 16.g5 winning a piece. I could not find any other move than 15...Nf8 fighting for a draw.
Anyone seen this move 15.g4 in another game? Any ideas how to proceed, or can Black better play another line?
Your replies are very much appreciated, thanks!