Great Grandma wants my son overnight.

My SO and i haven't had a night by ourselves sense my son was born and our relationship is having troublesome because lack of spending time with eachother and being close and doing things WE want to do alone. She offered to take him for 1 night and i trust her but idk if hes to young (15m) I really think this time alone is needed but at the same time i dont know.. would you guys let your babies go that young? My SO keeps saying "Fuck no" just because he use to not like her.. idk if i should let him go or just wait i guess.