If I have a 5-kg box on a 10-kg sled, do I need to consider the sled?

I have a physics problem, where a 10-kg sled rests on frictionless snow, with a 5-kg box on top of it. I need to know the maximum tension force on a rope tied to the sled without the box sliding back. I know the coefficient of kinetic friction, but since the question says the snow is frictionless, the sled shouldn't factor in, should it? The max tension should equal the max force of kinetic friction, right, otherwise it would slide back.