In AUTO mode the AFDS max bank angle is a function of TAS. At 250 kts TAS and below the max angle is 25 while above 250 the max angle is limited to 15 degrees of bank. The commanded angle varies according to the TAS up to the pre-programmed max value of 15 or 25.
Switching to manual, the max angle is whatever is selected regardless of airspeed.
This control is common to all aircraft from the 737 through the 777. The 747 includes inputs from flap position and computed V2 speeds in its bank angle limit computations for the AFDS.