Curious to know the answer to this also
I would think you would want to use a heavy-duty sewing machine. I used to have an old Singer 99K(3/4 size and meant as a machine for young ladie to use) It was very heavy to carry, but I swear would sew through concrete! I'm now very sad I gave it up! It might help if you had a welting foot for your machine and definitely use leather sewing machine needles as they have bladed sides that help with the puncture. Since I'm guessing you have 3 layers, start slowly and run it by hand for the first few stitches, to make sure it will go and then don't hurry around it too quickly. You also might want to rethink the thickness of the leather.
Best of luck!