Go back to basic training, think of the lift vectors, and how it tilts in a turn. To keep the same vertical component you need to increase the total lift perpendicular to the aerofoil because it is now banked. The lift is increased by increasing the angle of attack. Take it to extremes and keep banking and increasing the angle of attack to maintain the vertical component and eventually you will exceed the critical angle and stall the aerofoil at the same speed.
IF you do not increase the angle of attack you will have less vertical lift and descend as you said, and the stall speed will not change.
Remember stall is a function of angle of attack.