Forking, but losing the game

Black to move. C8 to get PGN.
This fork # 15.1 is explained in ebook Fork, a common chess pattern on Amazon.com , by Rodolfo Pardi.

For additional training on patterns, you can visit this page of mine: Patterns

Event:
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White:
Black:
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Side to move:
Last move:   variations:
Next move:   variations:

Move comment: