Power input regulator voltage range? Researching adding USB PD support

So I have this BPI-R64 on hand that has moved between different projects and have a new, hopefully more permanent one I am working on. Part of this is I’m trying to see about modifying it to accept USB PD input.

Looking at the RT6206 (12-5/3.3V DC-DC chip in the schematics) datasheet it has a wide 4.5-18V input range. The plan is to use an external PD trigger board to get the desired voltage from whatever PD supply is being used. Now some will say ‘just go 12V!’ which would be the simplest route. However officially 12V is not a standard voltage per current PD specs. So my thought was going 15V with the understanding that this is a set maximum and can drop down to 12/9/5 depending on the supply.

Any thoughts from the BPI-R64 side on this? I’m also wondering if there’s any concerns with how low the input voltage can go and be usable. I know on some different types of regulators there’s a minimum input voltage that needs to be a certain amount above the output but not sure if that’ll apply to this one. For example if a 5V supply is given, will that be suitable given the R64 converts internally to 5 and 3.3V. Obviously ample current/amperage will be needed.

After some further review of the schematics and datasheets, I think my plan of action will be sticking to 12V on the PD side even if it is non-standard. Most of my PD supplies and power banks support it anyways. Given the input filter cap on the board is only rated 16V, that’d be dangerously close to the limit feeding it 15V. The only gotcha would be if I run any supply that cannot do 12 and falls back to 9V. Should still be within acceptable voltage in theory, just needs to be capable of supplying enough amperage. Still getting the rest of my components together to get the final build set up and then I’ll do some power draw testing and see what the numbers tell me.