I don't see such a large difference in price.
I have 5+ S&S items, and it would be $46.93 for me. I backed into the $56.31 from the starting price of $93.86 and substituting a 5% S&S discount for the 15% with 5+ items. The difference is $9.38, which seems right - it's within $0.01 of 10% of the starting price.