dc5000 fill time?

i just bought a dc5000 i did some research from minitruckin mags when they did the tests and ti says it fills up in 1 1/2 mins in a 5 gallon tank iu think thats suprising is that wiuth a empty tank or when the tank fills and they go up and down and let the compressor fill again i let my car run for 15 mins and it still didnt fill all the way.