Based on the provided data, the coin in question has a grade of 70 (MBC-), and has had starting and final prices in previous auctions ranging from 8 to 250 euros. The average starting price in previous auctions was 53.31 euros, while the average final price was 78.89 euros.

Considering that the coin has been auctioned 135 times in the past, with a total of 118 sales and 17 times it did not sell, we can see that there is considerable interest in this coin among collectors.

Given that the starting price for the next auction is 15 euros and the maximum estimated purchase price in previous auctions has reached up to 250 euros, and taking into account the grade of the coin, we could estimate a maximum purchase price around 200 euros. This price would be in line with previous final prices and the interest this coin has generated in past auctions.

Therefore, my estimation for the maximum purchase price for this coin in the next auction would be around 200 euros.