Unable to unlock iPhone15 Pro by swiping up and Face ID

• Press and quickly release VOLUME UP

     then

• Press and quickly release VOLUME DOWN

     then

• Hold the SIDE button until an Apple logo appears (15-30 seconds), ignoring "slide to power off" if it appears

The operative word here is QUICKLY; and try it a couple of times, the timing is a little tricky. If done correctly this will always work unless the phone has a hardware problem. 

I don’t see how you can charge through a tablet.

It’s time to contact Apple Support:

• • Click on “Support” at the top or bottom of this page
  • Go to Contact Official Apple Support

(Note that both of the above have options to receive a callback or chat)

• • Call Apple Support; the phone numbers are in this link→Contact Apple for support and service - Apple Support
  • Make a Genius Bar appointment at an Apple Store→Genius Bar Reservation and Apple Support Options - Apple
  • Find an Apple store or Apple partner service provider→Find Locations

It should work unless your device has a hardware problem. Each press and release must be quickly, but you can take a few seconds between each press.