What is your goal weight and current weight?

BMR - 1467. Assuming that is more accurate Mifflin calc.
MFP at Lightly Active non-exercise maintenance - 2054.
1 lb weekly loss 500 cal deficit - 1554.
Which is reasonable right now.

So currently eating 25% deficit on non-exercise days. Much less on workout days because you eat more with no extra deficit, which sounds like most of your days.
I'd bet your weekly deficit on avg is only 17%.

What HRM model are you hoping is giving you good calorie burn info? And how long doing cardio getting fit?

What is your total, not net, gross eating level on average? So take a week of totals and divide by 7. You might be surprised where you already are eating at.

Do you weigh all the food you eat, measuring only liquids?

So eating level already up there at almost 1800. That's good.
Taking Lightly Active non-exercise calories 2054 + 357 avg daily burn (2502/7) = 2411 TDEE (higher than your estimate)
So indeed your total deficit on average is 25%.

But I'll bet it was more actually.

So 8.285 cal per min average burn in exercise.

That would normally be workout on easy end, does it feel easy for you?

For instance, basing this on more accurate than HRM walking formula, you'd have to walk about 7.5 kph (4.65 mph) flat to equal that lower calorie burn.
http://www.exrx.net/Calculators/WalkRunMETs.html

Perhaps that is how easy the workout is for you. But if it feels like much more than that, then ....
If you are decently fit, then your Polar is badly underestimating your calorie burn, and you are burning much more than you and it thinks, which means creating an even bigger deficit.
So more than 25% when you consider not eating back all those exercise calories.
More than the 77 calories daily you missed really netting 1500.

Might do this test next time, because if you know you can trust your HRM for calorie burn, then you can do the math I did above for your TDEE estimate, which is higher than your estimate.

http://www.myfitnesspal.com/topics/show/774337-how-to-test-hrm-for-how-accurate-calorie-burn-is

While waiting to do that, I'd suggest with a deficit of at least 25% and likely more for awhile, you start increasing calories eaten from 1500 daily to 1600 daily.
Wait a couple weeks, then add another 100 daily for a week or two.

Eat back your exercise calories, at least enough of them to hit that 2411 (or likely higher when you find out how off the HRM is).

This will slowly start letting your body know it's getting food, and it can adapt back up in metabolic speed.

And since you measure everything instead of best method of weighing, you likely are eating more than you think, so that may offset the under-reported exercise calories - but we'd never know.

Recommend you get a food scale and start weighing all your normally measured portions so you can see how much you have really been eating. Notice calories is per gram, 9 calorie per gram of fat, 4 per gram for protein and carbs. Not by volume, but my weight.

Wait - you have a Fitbit!?

Don't waste time trying to guess the correct rough TDEE from 5 levels.

You have a device designed to tell you your personal TDEE every day.

You must merely correct it for non-step based things like elliptical, and so HRM is great tool - if it's trustworthy of course.

So you merely need help with taking a reasonable deficit then to whatever you burn daily.

2400 or there abouts TDEE with 15% deficit is 360 cal deficit.

So Fitbit should have positive and negative syncing enabled.
Keep manually logging those workouts to correct Fitbit underestimated calorie burn.
Change your weight loss goal to 1/2 lb weekly.

Change your macros to whatever you want, but at least do the following.
Note the fat grams given, you want to keep those.
Note the protein grams given, you want to double those.
Lower the carb % until the protein grams are doubled as that % goes up, whatever % causes that to happen. Confirm fat stayed the same grams.

Now when you eat, you know you can miss your goal by 100 calories under to hit that 360 deficit which is reasonable for now.

When your Fitbit daily burn starts averaging out about 1650, then you need to start hitting your goal, keeping that 250 cal deficit.
Then take that to goal weight.

So that's the end game, my suggestion for getting up to TDEE for a reset is still best method, but use the Fitbit for it's TDEE now.