Rate of roll would normally be expressed in degrees per second - if you are rolling at 15 degrees per second, it will take you 3 seconds to change the angle of bank by 45 degrees, for example.
Think of the Airbus acting like a non FBW aircraft on the ground, where the movement of the side-stick is directly reflected by movement of the associated control surfaces (this is not entirely true, as you've stated above it's mediated by airspeed, but close enough). Once the transition is made into flight mode, the movement in control surfaces is whatever is required to achieve the commanded maneuver - e.g. referring to roll, if a 5 degree per second rate of roll to the left is requested by the pilot (by displacing the SS slightly to the left), the related control surfaces (ailerons and flight spoilers if applicable) will move to the extent that a 5 degree per second rate of roll will result.