cool_hardware52
Contributor
Never more than a 5 mil, usually a 3 mil. As you mentioned there's not enough compression at 15ft to compensate for the 5lbs or so of gas used.
As noted in my prior posts I qualify my weighting suggestions with a very specific set of gear.
A thick suit will loose considerable buoyancy from the surface to 15 ft. This loss of buoyancy offsets the weight of the 6-8 lbs of gas in a typical single cylinder.
Tobin