good chance you’re doing the same workout on the treadmill. You need to increase intensity or duration, I would say increase intensity. If you’ve done the same workout on the treadmill for 3-4 months, your body will adapt to it and you will get diminished returns. No if ands or buts
calorie estimates on a treadmill are always exaggerated to help encourage use and good feelings
I would recommend adding in heavy weight lifting to help shift your body composition. If you are 6’1” 180 lbs and 20% body fat, you don’t have enough muscle. Harder to build muscle while cutting and fasting but still build that habit up
as your weight has decreased, so has your daily calorie “requirement” and therefore your calorie target for weight loss
To summarize, in my personal non expert opinion. Drop your calories to 1300-1400 rather than 1400-1500. Increase the intensity of your cardio, and add in weight sessions