On the first day, one small ship carrying 24 sacks of rice reaches Kaifeng.
On the second day, five small ships carry 120 sacks of rice to Kaifeng.
On the third day, six medium-sized ships carry 360 sacks of rice to Kaifeng.
On the fourth day, seven large ships carry 840 sacks of rice to Kaifeng.
If this pattern continues, how many sacks were imported from day 1 to day 15?
Note: Kaifeng was the imperial capital of the Northern Song Dynasty