Well there are a lot of factors here.
I'll mention just a few.
Food: 1500 calories or under is probably too little for you, especially combined with the amount of exercising you're doing. You might have shocked your body into not losing weight. Also nutrients are important - you don't say how you're balancing your nutrients or how you're tracking them - having that information would help.
Exercise: I think you're over exercising, to be honest, and not doing the right kinds of exercise either. More about that later.
Age: I'm 42 and let me tell you that losing weight in your 40s is a WHOLE DIFFERENT BALL GAME. It sucks - to be blunt.
You have to work harder at it and be more committed than when you were 20 and could drop weight just by skipping dessert a few times a week.
Smoking: Quitting smoking, depending on how long you've smoked and how heavy a smoker you were is a HUGE change for your body and it could be another factor here. Nicotine not only suppresses appetite, but it does raise your metabolism to a degree. When you quit smoking you've lost that rush that helps burn calories.
Other factors: Sometimes even though your weight on the scale doesn't change, you're still losing fat. But there are so many things that affect what the scale says. You can retain fluid from exercising, retain fluid from sodium intake, retain fluid from too little water. It could be that time of month for you, or you could be ovulating. Heck, the barometric pressure could be changing. My weight can fluctuate up to 10 lbs over the course of a month from all of those things.
Also I've found that a lot of people don't lose weight at a steady pace. I"m one of those people who loses in fits and starts - I'll hold the same weight for 2 or 3 weeks and then WHAM - the scale will show 6 lbs gone. It's not that I lost it all in that week, but that my body just has to have time to readjust.
Bottom line is that your body is probably reeling from all the changes you've put through it and there are a lot of things that could be going on that are changing in your body but not showing up on the scale.
Here is what I'd suggest:
Ditch the Alli. It doesn't do anything for you except force you to do what you should be doing already out of fear of the side effects. And it doesn't help with retaining nutrients.
Food: Eat 1800-2000 calories a day and make sure you get at least 120g a day of protein. Make sure you're avoiding all simple carbs and eating complex carbs (should be around 40% of your calories) - things like whole grains, oats, and so forth. Make sure that at least 20% of your diet is healthy fats from things like olive oil, nuts and seeds, avocados, etc. Register with someplace like fitday.com or thedailyplate.com to make sure you're accurately tracking calories and nutrients.
Exercise: Scale back on the cardio. Look into the weight lifting threads sticky posted at the top here. Especially read the one about weight lifting for women. Do a good, intense round of weight lifting and/or body weight exercises 2x-3x a week and then fill in around that with cardio for 30-45 mins a day. You can mix up interval training with regular ss-cardio - whatever works for you. Be SURE to take a full day off each week to give your body time to recover and be sure to leave at least a full 48 hours between your weight lifting / bodyweight exercises.
Make sure you're drinking plenty of water - the American Sports Medicine Institute recommends as a starting guideline that you drink 1 oz of water for every 2 lbs of body weight - so for you, around 110 oz per day is a good figure to shoot for.
And mostly, give it time. Try taking measurements (bust, waist, hip, thigh) as well as measuring on the scale. Sometimes the measurements are more telling than the scale.
