Oliver's $20 bills amount to $20 x 10 = $<<20*10=200>>200.
Oliver's $5 bills amount to $5 x 3 = $<<5*3=15>>15.
So, Oliver has a total of $200 + $15 = $<<200+15=215>>215.
William's $10 bills amount to $10 x 15 = $<<10*15=150>>150.
William's $5 bills amount to $5 x 4 = $<<5*4=20>>20.
So, William has a total of $150 + $20 = $<<150+20=170>>170.
Therefore, Oliver has $215 - $170 = $<<215-170=45>>45 more than William.
#### 45