Using the GRL-C2 USB PD Tester and GRL-PSP Power Analyzer software from Granite River Labs, we can see that the Apple iPhone 12 Pro (with display kept on) uses the most power under 10% battery, uses a reduced power level from 10% to 90% battery, and gradually reduces power after 90% battery, taking about 2.9 hours to charge the phone to 100%. Note that the iPhone 12 Pro still continues to charge the phone for some time even after reporting 100% battery. The iPhone 12 Pro stays under a comfortable 37 degrees throughout the entire charging cycle.
We see that below 10% battery, the Samsung 15W Wireless Charger Stand draws a max 12W from its USB-C port over USB Power Delivery, meaning the iPhone 12 Pro is getting about 7-8W over Qi wireless testing. From 10% to 90% battery, the Samsung 15W Wireless Charger Stand draws about 10W over USB-C, with the iPhone 12 Pro receiving about 6-7W over Qi.
Unlike with the Apple MagSafe Charger, the iPhone 12 Pro doesn't employ power management schemes with the Samsung 15W Wireless Charger Stand that deliberately slows down power charging after 70%. If you actually want to achieve fast charging times and charge your phone to 100%, the Samsung 15W Wireless Charger Stand is actually a better option than the MagSafe Charger.