So I bought a naish arx 15.5 with a 18" liquid force bar for $250
Would have to agree, that's a very old kite (2002 I think) and a terrible kite to be learning on compared to more modern kites.
It's not just a case of "latest and greatest", kites manufacturers have made some massive technical gains every year, but most people would agree that 2006 was a breakthrough year. You will find it a lot easier to learn with a post 2006 kite, preferably a Bow/SLE/Flat style kite.
If you're determined to stick with it, the reason that kite is falling out of the sky is called hindenburging. The kite flies too far forward in the window, loses lift, turns over and falls. Modern kites are far less prone to this, simply sliding back into the wind window and thus staying in the air.
To prevent that with an ARX in light winds, you're going to have to keep the kite moving (or yourself moving). Don't park it at 12 o'clock in light/gusty winds.