How do you know you are losing 15 lt per minute...it would suggest that you are using the meter to calculate this figure. Which then tells us that the leak is after the meter, which means its your problem.
Between the meter and your property is your bit.
...15 lt per minute... is 900 lt per hour.
900 ltrs is just short of 1000 ltrs which equal.. 1 cubic metre.
You pay for your water in cubic metres...
(Our water is approx 90p per cubic metre)
Which means it's costing you around about £1 per hour...day and night.
More bad news ...they also charge you a fee for waste water ...So if the water is going past the meter, they charge you for disposing of it, even if you have'nt used it.
Someone needs to dig a hole, and find it soon.!
Why not be green and thrifty......fill some bowls and the kettle...it's easily turned off at the meter, and just turn it on when you need it..Certainly turn it off at night and straight away you have halved your loss.