How about playing 15...dxe4 instead of 15 ...Nh7? Then, after some exchanges (for example, 15...dxe4 16 Nxe4 Nxe4 17 Bxe4 Bxe4 18 Rxe4 19 Qf6) you could play Qf6 to defend your king, and have a safe advantage.
In the game, 15...Nh7 allowed White to take over the center with 16 cxd5 and make your Bb7 ineffective.
The critical moment is really Black's 10th move. After
9. Ng5 h6 10. h4
you're opponent is telling you that he thinks you can't take his knight without suffering some pain. In this type of position, it's always important to calculate closely and see if your opponent is right. In this case, you can clearly predict the following moves:
10. ... hxg5 11. hxg5
This forces you to move the knight. Imagine for a second that the knight is not on the board. What is white's "threat"? The only thing he can hopr for is to play 12. Qh5 threatening mate on the h7 square. He is relying on the open b1-h7 diagonal for an attack. The question now is can you move your knight and eliminate the threat on the h7 square? It turns out you can as after 11. ... Ne4, White has no further attack and you have a knight for a pawn. Also note that the g5 pawn is now under attack. There is no way for White to displace that knight other than to capture, and after Nxe4 dxe4 the threat on h7 is gone forever. If your opponent tries 12. g6 attempting to bust open your King position, then his h2 square becomes weak and the move 12. ... Qh4! is very strong, threatening both f2 and h2. At this point, Black has a significant advantage and should win easily.
The bottom line is never respond to an attack on the h7 square with fear. Many players try this and usually such an attack will fail. You should rise to the challenge of proving them wrong.
Make sure you turn on "move list" before examining this game.
I was playing Black. I don't see any glaring mistakes in the game for me, but maybe some of you will. I fought hard, but lost in the end. Good game.