The backspace on the rims should work pretty well with your combination.
For the tires, the back should work just fine as long as the rear of your car is stock height or higher. A little more backspace would probably be better, but as long as you're not lowered that combination should fit most Dusters set up like yours.
In the front I think you may have issues with the tire height. Again, it will depend on your ride height but a 205/70/15 is 26.4" tall, and to be safe you should generally keep them under 26". A 215/65/15 would be 26" tall, a 225/60/15 would be 25.6", and both should work on a 15x7 with a 4.25" backspace and 73+ style mopar disks.