Compared to Cambodia, sure, but it's an international crime gang, with this particular one being just one branch. I wonder if this was their biggest hoard or if they had more?
Really poor financial management to have all that money concentrated that much though. It either means they dropped the ball bigly, or this is spare change for them... although Bitcoin's market cap is $2.24 trillion at the moment, $15 billion is a significant chunk of that.