OK, let's work through this together. We're starting with 863 and we're going to multiply it by 15, which means we add 863 to itself 15 times.
Step 1: 0 + 863 = 863
Step 2: 863 + 863 = 1726
Step 3: 1726 + 863 = 2589
Step 4: 2589 + 863 = 3452
Step 5: 3452 + 863 = 4315
Step 6: 4315 + 863 = 5178
Step 7: 5178 + 863 = 6041
Step 8: 6041 + 863 = 6904
Step 9: 6904 + 863 = 7767
Step 10: 7767 + 863 = 8630
Step 11: 8630 + 863 = 9493
Step 12: 9493 + 863 = 10356
Step 13: 10356 + 863 = 11219
Step 14: 11219 + 863 = 12082
Step 15: 12082 + 863 = 12945

So, 863*15 = 12945