It seems to be the case that you can not power the xiao nrf54l15 from the 3V pin and get ~3uA current draw in all cases. @msfujino and I both saw as you did that the current draw is ~450uA at 3.0V. At higher voltages on the pin, you get the expected current draw. @msfujino discovered that the switchover point is ~3.3v.
This means the xiao nrf54l15 doesn’t look like a good candidate for non-rechargeable batteries such at the CR2032 and CR123A where the voltage is below 3.3V.
I’m sticking with the xiao nrf52840, which works with non-rechargeable batteries, for now for my matter application. I’ve ordered a few holyiot nrf54l15 modules and will give those a try.