To check impulse you will need more information you will require more data as it was diverse with time. In this question, there are two balls with various mass and speed, along these lines they have diverse force. I will expect you are getting some information about the momentum.
The momentum of ball 1 should be:
momentum 1 = mass₁ x velocity₁
momentum 1 = 2kg x 10m/s = 20kg m/s
The momentum of ball 2 should be:
momentum 2= mass₂ x velocity₂
momentum 2= 1.5kg x 20 m/s = 30kg m/s
The answer would be "1.5kg ball because it was travelling faster".