Let's roll up our sleeves and solve this. We have 591 and we're going to multiply it by 15, essentially adding 591 to itself 15 times.
Step 1: 0 + 591 = 591
Step 2: 591 + 591 = 1182
Step 3: 1182 + 591 = 1773
Step 4: 1773 + 591 = 2364
Step 5: 2364 + 591 = 2955
Step 6: 2955 + 591 = 3546
Step 7: 3546 + 591 = 4137
Step 8: 4137 + 591 = 4728
Step 9: 4728 + 591 = 5319
Step 10: 5319 + 591 = 5910
Step 11: 5910 + 591 = 6501
Step 12: 6501 + 591 = 7092
Step 13: 7092 + 591 = 7683
Step 14: 7683 + 591 = 8274
Step 15: 8274 + 591 = 8865

So, 591*15 = 8865