Trailer Light Wiring Using Fuse Tap?

We have a 2019 AWD-E XLE. I'm adding trailer light wiring to tow a combined weight (trailer and cargo) of less than 500lbs. I have the CURT 56439 no splice wiring kit which requires a 15 amp power supply to the wiring converter box.

Running the power wire all the way from the back of the vehicle through the firewall to the battery seems to be (for me) very difficult. I'd prefer to use a fuse tap on the interior fuse panel. There are a few unused slots (12, 18, 23, 28, 29, 30) on the interior fuse panel which would appear to be a good source for the converter box and they do test with unswitched 12v power. However, none of the diagrams I can find (including on Fuse-box info) show what amps those open slots are rated for.

Does anyone know what amperage these open slots are rated for, where I might find that info, or how I can determine myself what amps the source power wiring will handle?

Thanks!