The SAE paper SAE J689 would tell us the nitty gritty, but isn't available freely online. Documents referencing it, for ambulance design criteria, cite a minimum approach angle of 20* a ramp breakover angle of 10* and a departure angle of 10* ... though presuming you'd want to get out of the same parking lots you got into, then I'd go with a 20* departure angle as well.
Municipalities should be designing their speed bumps and curbs with these recommendations in mind, as should major institutions wrt to their parking lots.. however, there's gonna be the odd sharp ramp still that you might have to avoid.
Basically, you imagine a 20* wedge, with the point at the point of contact of your front or back wheel, any bodywork inside the wedge is baaaad mmmkay. Then take a side photo, and make a 170* angle (10* breakover) and slide it with each arm in contact with the bottom of the tires, such that the angle describes an arc from one wheel to the other, keeping the wheels in contact with the arms... now anything inside that arc is gonna hit, anything above it will be okay.
So if you lower them such that you've got a 20* wedge front and rear and can sweep an arc with the apex of the 170* angle between the wheels, then you should be okay 90% of the time, barring snow, unmade/gravel roads etc.
However, this doesn't take into account ride comfort and allowing enough suspension movement to handle safely, also note, that you really wanna aim for these parameters with the car loaded, not empty.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice