I used to carb 500ml and 1liter bottles and it lasted awhile. I thought I read that a 20 ounce tank will carb and push 1.5 corny kegs of beer around 12psi. Or 1 keg of water around 25psi and push. So the above statement that it did 15, 2 liter bottles would holds true.
20 ounce tank should do around,
1, keg around 25psi,
15, 2 liter bottles,
30, 1 liter bottles,
60, 500ml bottles,