Where in North Phoenix are you (SE Gilbert here…)? That seems like and AWEFULLY high clay concentration for Arizona.
This thread is the BEST for calculating the drip settings. If you follow the directions, you should be able to get a PR (in/hr) that works well. Main thing to start with is dialing in your soil though, and again, I struggle with that clay content for the valley.
For reference, here are my old settings from when I set mine up. I have 1gph emitters on my shrubs, which equates to a .30 in/hr, which has my shrub zone running for right at 4h each time, but this is based of my clay loam soil (not to be confused with heavy clay).
Square footage does nothing other than calculate estimated water usage, nothing related to actual watering. 15" might be a tad deep for anything but the most established and strong shrubs. I have mine set at 12" right now, but I have a mix of well established and newer planting shrubs, and you need to cater to the more needy.