at my kickboxing gym we spar with 16oz
At my boxing gym where we throw a bit harder with the hands we always spar with 20oz, which I'm told is pretty standard as far as boxing sparring goes
Really I don't see a point in NOT sparring with 20oz gloves unless the spar was specifically to simulate fight conditions. The point of sparring is developing stamina and muscle memory of techniques and reactions. Putting on heaviest gloves allows you to put more effort without hurting eachother, get more stamina, and slow things down too to work with eachother.