To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Starting Price: 1500 euros.
2. Condition: The coin has a condition rating of 85 (MBC+/EBC-), indicating that it is in fairly good shape.
3. Auction History:
- It has been auctioned 5 times in the past, of which it has sold 4 times.
- The average hammer price in previous auctions is 1775 euros.
- In the 2021 auction, with the same condition (85), it sold for 1600 euros.
- In the 2015 auction, it sold for 1200 euros, and in the 2024 auction, it sold for 2000 euros with a condition of 80.

4. Price Trends: The average hammer price has been increasing, and the highest recorded hammer price is 2000 euros.

Based on this data, the estimated maximum purchase price could be in a range between the average hammer price (1775 euros) and the highest recorded price (2000 euros). Given that the coin's condition is good and the starting price is 1500 euros, a reasonable maximum purchase price could be:

Estimated maximum purchase price: 1900 euros.

This price reflects a balance between the price history, the current condition, and the upward trend in hammer prices.