Sort:  

I wasn't in crypto at that time - just looked at your charts.

I wasn't either to be fair, starting trading at the end of 2016.
Checked what caused the August 2015 dump, apparently it was some FUD around a Bitcoin fork:
https://cointelegraph.com/news/bitcoin-xt-fork-can-blacklist-tor-exits-may-reveal-users-ip-addresses

The market was very illiquid back then though.