charging my IPad pro 2020 4th generation

A lower wattage power/charger will charge your iPad, but at a much slower rate, taking more time charge your device.

You are best advice to use the Apple charge cable and Apple power/charging adapter block that came with that iPad model.

Apple ONLY makes a lower 12W power/charging adapter.

If you are using a non-Apple power/charging adapter that is rated at 15W, as long as the rated voltage is 5V, it should be fine to use with your iPad Air 4.

You will do no damage to your iPad Air.