For me, this is a such a huge amount worth of Bitcoin to be moved in another address in only 15 minutes. However, it's still a mystery whatever the reason is.
These whales are just fortunate enough to accumulate Bitcoin during the early times. Until now, I still regretted in doubting about investing in Bitcoin years ago.
Correct me if I'm wrong, but these whales know what they are doing. They are here for the long-term since they have enough BTCs in their arsenal, especially the next year's halving. However, I would not really count on halving's guarantee of BTC's price pump.
It's likely not a whale but an exchange consolidating it's accounts. If they have a lot of dust they will move it to consolidate it into fewer addresses.
Most bitcoins are held at the major exchanges rather than in whales wallets.