When I first got certified, I was using air at or close to that rate. It took me a while but the first thing I realized was that I was way over-weighted. I incrementally reduced the lead I was carrying until I got it down to where I didn't have to put nearly as much air in my BCD to get buoyant. This reduced my drag. When my wife got certified the year after I did, she complained because she couldn't keep up with me. That's when I realized diving is not a race and when I slowed down, it reduced my air consumption even more. And actually paying attention to your breathing rate and practicing slow steady breathing, even when out of the water, will help. One other thing that you probably don't realize at this point in your diving is that although you think you may be relaxed when diving you're really not as much as you think you are. But that's to be expected as breathing underwater is not natural for us. It takes a while to get used to that, too.
Now my SAC (or more accurately RMV) is consistently in the low .4 range, sometimes even dipping into the mid to upper .3s. And I'm a big old guy (6 ft, 245lbs, 68 years old).
Be patient. Make sure your weighting is right, work on your trim, slow down, relax, and practice breathing. Your air consumption will eventually improve. There's no set time as to how long it will take. That will depend on how much you dive and how much you work on it to get these things worked out to make sure you are as efficient in the water as you possibly can.
