If any fiat currency would go down 15% we'd call it a crash.

USD/GBP fell 19% after the brexit-referendum, that was an abnormal noteworthy event with quite far-reaching consequences.

For BTC it's a daily occurence...

"Crash" of an asset/currency is always against other assets/currency -- you need to define what its comparable otherwise you can not measure it.

Was it a "crash" though in scope?

Black Friday in 1987 was a 22% drop in the stock market. Yesterday was a 14% to 18% drop depending on how you calculate it. Close to what was considered a prototypical "crash": https://en.wikipedia.org/wiki/Black_Monday_(1987)

Basically BTC is highly volatile, thus it probably crashes all the time based on standard definitions.