Gas consumption on a 6kg bottle

Hi, can anyone help, we are new to motorhoming and have just come back from our first trip. We had a full bottle of gas and only really used it for cooking (used the oven once and the hob a coulpe of times) and the bottle was empty by the 3rd day. We also used gas once to warm the water heater for about 15 mins. Is this normal or do we have a problem with the gas, we did not expect to use that much gas !! What could be the possible faults ??