Don't you prefer my Nxb6 decision?

Computer doens't like it, but, instead of winning an exchange, I go for burrying their LSB on a8. (It's a 960 game.) Makes sense to me. What do you think?

Otherwise, a7-a6 creates a scape square for the DSB and soon the LSB could be released.

I agree with your decision to be honest. Positionally speaking, you're up a piece as opposed to an exchange. As long as b5 remains solid as a rock (which it is), this is probably better because the piece will stay buried.

The computer thinks both options are easily winning.
15.Nxf8 Rxf8 16.Qh4 would pick up the knight on g5 as well, leaving you a full rook ahead.

@Sandstad
That is true, I could win a piece besides the exchange. The line I chose seems to allow some escape for that piece.

In which case, difference in evaluation wasn't much, so it seems generally better to burry a minor piece, than winning an exchange.