Based on the data provided, we can observe that the coin has had an average auction closing price of 71.17 euros in previous auctions. Additionally, the current condition of the coin is graded at 75 (MBC).

Considering that the starting price for the upcoming auction is 15 euros and the historical average closing price has been 71.17 euros, we could estimate a maximum purchase price around that range. Given that the coin's condition is 75 (MBC), which is considered quite good, this could influence a higher purchase price.

Therefore, an estimated maximum purchase price for this coin in the next auction could range between 60 and 80 euros, taking into account its previous auction history and current condition.