I used the word probably which is a guess that there probably more potential collectors than coins to satisfy the potential demand from that amount of collectors. 15000 is not a huge amount of coins for example a 1905 half crown has a published mintage of 166008 and you would require a lot of money to obtain a good example. It's called supply and demand. Maybe there are more collectors of half crowns than florins and as the 1905 half crown was issued for circulation less of the total would survive in good condition but even a worn example attracts a fairly high price. Recently I saw one for sale in fine condition for GBP 440.