To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Condition: The coin has a condition rating of 70 (VF-), indicating that it is in an acceptable state, but not in the best condition.

2. Auction History:
- It has been auctioned 14 times in the past, of which it has sold 11 times.
- The average hammer price in previous auctions for coins with the same condition (70) has varied, but it can be observed that it has reached hammer prices of up to 35 euros in the past.

3. Starting and Hammer Prices:
- The current starting price is 15 euros, which is a relatively low price compared to previous hammer prices.
- The average hammer price for similar coins has been 27.09 euros.

4. Trends:
- In previous auctions, hammer prices have ranged between 20 and 35 euros for coins with the same condition.
- The trend shows that, despite some lots not selling, those that did reached prices that exceed the current starting price.

Based on this information, an estimated maximum purchase price could be set in a range between 30 and 35 euros, given that this is the range it has reached in previous auctions for coins with the same condition.

Therefore, a reasonable estimated maximum purchase price would be 35 euros.