[Spice and Wolf] When does the story take place?

Early in the series, when the main duo are staying at a church, Lawrence pays for potatoes and goat cheese. Potatoes are a new world crop, which would put it after 1492, but I'm curious when exactly. I know that potatoes took some time to become popular in Europe, and were originally used as livestock feed. So is this decades after 1492, or is lawrence just being thrifty?