https://en.numista.com/catalogue/contributions/modifier.php?id=71689
All modern US silver commemorative dollars are issued in 2 finishes: Uncirculated and Proof (often, by different mints, though, in this case both are P), so we need another line added for the 2015 P Proof.
Also, the mintage being shown as 500,000 - that is misleading. That number is the maximum mintage authorized by the US Congress across all product options. Final mintage is usually quite a bit lower and we won't know what it is until sales stop on Dec. 31 (any remaining unsold extras will be melted at that time).