It's entirely sustainable @savedbythewell, but it's boring. In fact, 1,500 calories is 500 calories more than necessary. I had a phase of ingesting 1,000 calories a day and lost a stone (I had an ED, so not necessarily advisable, but easily possible).
Breakfast: One Shredded Wheat with semi skimmed milk (leave the milk in the bowl).
Lunch: tuna sandwich using two thin slices of wholemeal bread. An apple.
Supper: anything, really (as the DC were still at home then so I didn't want to model disordered eating), but a very small portion of whatever it was.
A pot of chocolate pudding to satisfy chocolate cravings (80 kcal).
Drinks: black tea, black coffee, herbal teas.
And lots of exercise (not the gym, as I hate them - walking and cycling everywhere, which adds up to about 10 miles per day).
Very boring, but perfectly do-able.