How many shots in 1.5litres of whiskey?

Depends on where you are.

In Europe, a shot is 20ml.

In the UK, a shot is either 25ml or 35ml.

In the US, a shot is one fluid ounce, roughly equivalent to 30ml.

So divide 1500 (ml in 1.5 litres) by the value of your choice from above and you get the answer...