Thank you.
I can't fix that one in a simple way, we don't have method to set the experience level of an unit we (re)create, we can set the experience points only.
I'm still thinking about the alternatives here. I could make promotions to not require an experience level, but then the units will get promotions too quickly.
I'll try to neutralize the vanilla XP gain and set/track a custom XP value to trigger promotion (IE give the unit 15 "real" XP points) when the custom XP reach a value corresponding to a custom "level"