To estimate a maximum purchase price for the coin in question, several factors must be considered, including the starting price, the condition of the coin, and the hammer prices of similar coins in the past.

### Relevant Data:
- Starting Price: 15 euros
- Condition of this Coin: 25 (BC)
- Previous Prices of this Coin:
- Coins with similar conditions (BC) have been sold in a price range that varies, but it is generally observed that hammer prices for coins in BC condition are significantly lower than for coins in better conditions.

### Analysis of Previous Prices:
- In previous auctions, hammer prices for coins in BC condition or similar have ranged between 20 and 60 euros, depending on demand and the rarity of the coin.
- Most coins in BC condition tend to sell in the lower price range, often below 50 euros.

### Maximum Price Estimation:
Given that the condition of the coin is 25 (BC), and considering the starting price of 15 euros, a reasonable maximum purchase price could be in the range of 30 to 50 euros. However, since the average hammer price for coins in similar conditions has been approximately 35-40 euros, an estimated maximum purchase price could be:

Estimated Maximum Purchase Price: 40 euros.

This price reflects a balance between the condition of the coin and the historical hammer prices for similar coins.