I vote calories in are being under counted.
In the end, it's just pure numbers. If you burn more than you eat, you will lose weight.
Reta will help you consume less, for sure, it may even help you burn a bit more in terms of increasing resting metabolic rate, but at the end of the day, week, month, if you're not losing weight you are consuming too many calories compared to what you're burning.
condiments, small snacks, beverages, it could be anything, but i'm confident there's something not being counted toward your daily intake
Dropping to 1500 is a bit extreme and if you can't stick with for an extended period, it it's not even worth trying because you'll rebound hard
I'd say if you're currently counting 1,950 daily, drop that to 1850-1800 (strict) and watch the scale.
Remember a pound of fat is like 3,500 calories. You'd need to be at a 500 calorie deficit for 7 days straight to lose one single pound. If you go over your cals one or two days, you could throw the whole week away.