Partially drain the juice from the peaches. Place peaches in a large mixing bowl and set aside.
Mix sugars, spices, flour, and salt substitute in a bowl. Add to peaches. Mix well.
Line a 9- by 12-inch baking pan with two of the pie crusts. Pour the peaches into the pan.
Scatter the cold margarine over the peach mixture, then place the two remaining crusts over the peaches. Pierce the top crust with slits to allow steam to escape.
Spray the top of the cobbler with vegetable spray. Bake for 15 minutes at 425 F then reduce the oven temperature to 350 F. Bake for another 45 minutes, until the cobbler is brown and bubbly.