i believe the rental places here on the mountains do front foot 15 and rear foot at 0 or -3 degrees if you dont tell them what degree you want.. so you might want to start with that and go from there. i usually put 15 and -3 for beginner friends that dont know what degree they want and it ends up fine.
Considering it's a twin board, I'd assume you'll want to ride switch. 15/-15 duck stance is excellent for that.
yea i agree with that but i think it really depends on what youve been riding before. and if it was rentals, most likely it isnt the duck. it took me a few days to go from 15/0 to 15/-15 with the same confidence while learning switch. i just raised it 6 degrees til i rode well with it, then raised it another 6, etc.