The truth about the acceleration of both object is this: THE ACCELERATION OF OBJECT B IS HALF THAT OF OBJECT A.
The statement above can be proofed by using the force formula, F =Ma
Where F = Force, M =mass and a = acceleration.
For object A, its acceleration, a = F/ M = 15/25 = 0.6N
For object B, a = 15/ 50 = 0.3N
This calculation shows that the acceleration of object B is exactly half of that of object A.