What kind of vehicle, car, truck, suv?
15” tires are a dwindling animal, depending on the usage and size.
As stated above, the taller the sidewall the more compliant ( comfort ) they’ll be, given certain parameters. A 70 series tire will be more comfortable than a 60 series, generally speaking. However, a 70 series H rated tire probably won’t be as compliant as a 60 series that’s S rated.
The speed rating will have a lot to do with comfort, the higher the rating, the more road feel you’ll feel. I forget the exact codes, but it used to be H 130, V 149, Z over 149. Now there’s W and I think Y, those are backets above 149 mph. Certain speed ratings will only be had in specific sizes, e.g. you won’t get a 235/60/15 tire in a W speed rating. I think....
Wheels are preference, but alloy is lighter than steel, takes less effort to move, thereby offering slightly better fuel economy all things being equal.
Keeping any wheel clean can be a PITA. The more ornate, the more annoying they become. Dirty wheels is also a function of the type of brake pad used. I always used factory pads, and they would dust the wheels sitting still. Switched to Hawk ceramic pads and did cartwheels come wash time.
Both alloy and steel bend, so if you have a habit of hitting curbs or can’t seem to avoid any potholes, you’ll be bending them. The lower the tire profile, the greater the chance of bending them. They can be straightened, but at a cost. If replacing, steel will be cheaper than alloy, or at least should be.
The tirerack has a tool to search tires by size. You can peruse that to see what tires cost in specific sizes and get an idea on what price points are.