@U235
Interesting look on his reaction, I'll share my thoughts.
Personally, my family's total annual income comes up to $20,000, so 15k really is a LOT. But that's the viewpoint of a person who grew up poor. How about someone who makes 80k annually. He made almost a fifth of their entire annual income in a single day by picking up a few rocks because he thought they looked pretty, AND he is holding all of that money in a single bag which means he isn't looking at numbers but cold hard cash.
In the viewpoint of people from this world, he made over double the cost of annual living expenses in a single day. (5 silvers is one months of living expenses.)
Keep in mind he had no idea about what the value of the things he picked were. It is usually common knowledge that a diamond or a car is VALUABLE. Unlike a rock where you have no knowledge about, found in a cave, and thought it looked pretty, would actually be worth 100,000 yen converted.