QUESTION ON PRESSURE?

hi okay, so for our chemistry cl, we are doing an experiment on pressure, and so we have 4 beakers, with the exact same amount of water in each, and we freeze all of the beakers. then we put them inside a bell jar, and pump it inside with a syringe, so that the pressure decreases. there was one wich we just left outside, our control, most pressure, one that we pumped 2 times, another pumped 4 times, and another pumped 6 times. in the end, the less perssure, melter faster. so our control was the one that melted the slowest, so the more pressure, the slower it melts, why is this? please explain in terms of chemistry or science THANKS