Perhaps if you're obese and your body can burn enough of its stored fat you could maintain it for a while, but 1500 kcal/day is too low for an active person - for most people it barely covers the BMR needs. In order to stop body from reducing your muscle mass you need to stimulate those muscles a lot, you need to use them hard, so your real caloric needs would be significantly higher. Big problem with such extreme restrictions is that in 6 months body will adapt to low calorie intake (shed the unneeded muscles, slow down metabolism), so if you ever decide to stop the program and go back to the normal dietary regime, you'll be in a big problem how not to get overweight really quickly.