2.5 million times 6 nurses is 15 million, equal to just just 3 diamonds.
Is the amount of diamond random per shot or did the nurses think or knew it's only 1 diamond per shot, if they were only planning to do it 3 times?
If it increases per shot and 1 came out on the first shot and 2 on the second then 3, 4 and 5 should come out of the next 3 shots.
At 5 million yen each, it should total (3 + 4 + 5) x 5 = 60 million yen. 10m per nurse.