Based on the data provided, we can see that the coin in question has had an average starting price of 34.8 euros in previous auctions, with an average closing price of 67.11 euros. The conservation of this coin has been described as 70 (MBC-), indicating a fairly acceptable condition.

Looking at the previous prices of this coin in past auctions, we can see that it has had fluctuations in its starting, estimated, and closing prices. However, the highest price reached in an auction was 260 euros.

Given that the coin will be auctioned in the coming days with a starting price of 15 euros and considering its price history, conservation, and demand, my estimate for the maximum purchase price for this coin would be around 200 euros. This is considering that it has reached that price in the past and that its conservation is relatively good.