Resuggesting under Xergoyf's comments:

My purchase was for 12 keys https://gyazo.com/f52f96f2c9f7eb01bc9810f315ca9dab

Considering both 10s were to buy orders, I would go for a conservative drop to 12. SCM buyers are around 11.5 as well, which support excluding the 10s.

Spelled, so excluding: https://backpack.tf/item/648364761

https://backpack.tf/item/9646268697

10k 15ref:

https://backpack.tf/profiles/76561198029644087#!/compare/1629158400/1629417600

12k - thanks to Xergoyf:

https://gyazo.com/f52f96f2c9f7eb01bc9810f315ca9dab

https://backpack.tf/profiles/76561199183541107#!/compare/1630108800/1630195200

https://backpack.tf/item/6197927835

10k 5.55ref:

https://backpack.tf/profiles/76561197994102903#!/compare/1624579200/1624752000

Snapshot suggests 12k, which keys leaving buyer's compare also support: https://gladiator.tf/listings/61228859569edc5024ea8c77

https://backpack.tf/profiles/76561198453530349#!/compare/1629504000/1629676800

https://backpack.tf/profiles/76561198291789666#!/compare/1629590400/1629676800 - other keys used to buy ghosts shako

Sales:

10, 10, 12, 12