Alright, so I'm using a lot of assumption here to fill in the blanks, but I'll see if I can offer some help...
At 5'6" and 140lbs, without knowing your age, I'll say you have a BMR of about 1433 calories.
I'll assume you have a reasonably sedentary job and multiply that by 1.2 to get a base daily energy expenditure of about 1720 calories.
Walking 2 miles (I'm assuming that's a total; 1 mile there and 1 mile back) at an average pace of 3mph burns about 125 calories.
I'll assume you work Monday to Friday, so you're burning those calories on 5 of 7 days.
You say your P90X workouts burn between 250-500 calories, so we'll just average it to get 375 calories burned during exercise.
I've never tried P90X, but a quick Google search seems to suggest that it's a 6 on 1 off schedule, so you're burning that average of 375 calories 6 of 7 days.
So, putting it all together... 1720 * 7 + 125 * 5 + 375 * 6 = Total weekly energy expenditure of 14915 / 7 days = Total daily energy expenditure of 2130 (maintenance).
Now, if you're normally eating 1500 calories a day, that works out to a weekly deficit of 4410 calories, which should translate to roughly 1.26lbs of fat loss per week. So, if you're not seeing any progress, then something is off... are you positive you're tracking calories correctly? A food scale can be a huge help in that department.
Otherwise, try adjusting your macro nutrient ratios. If you're getting between 10-15% of your calories from protein, and you're eating 1500 calories, then you're only getting between 37.5-56.25g protein. That's on average 0.74g/kg of body weight. I know some people on here will disagree with me, but that's just too low... you're quite active, and with goals of losing fat and gaining muscle, you should be aiming for at least 1.5g/kg, which works out to about 95g per day. Add some tofu/tempeh/beans, like you mentioned, or even pick up some protein powder.
1.26lbs per week is a safe rate at which to lose weight, so I think you're fine to continue eating 1500 calories. If you get 95g of protein, that's 25% of your calories, which means that you'll need to adjust the rest of your macros. Try aiming for 55% carbs, 20% fat, and 25% protein. If you're still not seeing results, bump the protein up to 30% and reduce the carbs to 50%.