There are other sales that've also happened recently.

https://backpack.tf/profiles/76561198083621911#!/compare/1743379200/1743465600 - Bulk

https://backpack.tf/profiles/76561198075499550#!/compare/1743984000/1744070400 - Quicksold for 13 Keys, probably with the 35 Refined as change

https://backpack.tf/profiles/76561198012514588#!/compare/1743984000/1744070400 - Quicksold for 12 Keys + 34 Refined

https://backpack.tf/profiles/76561198349848918#!/compare/1742428800/1742515200 - 14 Keys

https://backpack.tf/profiles/76561197975587947#!/compare/1743638400/1743724800 - 21 Keys, but this is a high outlier because...

https://backpack.tf/profiles/76561198382237103#!/compare/1745884800/1746144000 - It was later dumped to quicksell.store who listed it for 18.43

https://backpack.tf/profiles/76561198355443649#!/compare/1743984000/1744243200 - Probably gambled

https://backpack.tf/profiles/76561199110412711#!/compare/1742601600/1742774400 - ?

https://backpack.tf/profiles/76561198049501416#!/compare/1743120000/1743465600 - ?

https://backpack.tf/profiles/76561199104559253#!/compare/1741910400/1742083200 - 14 Keys

https://backpack.tf/profiles/76561199581722058#!/compare/1745798400/1745884800 - 13 Keys + 0.44 Refined

https://backpack.tf/profiles/76561199551005632#!/compare/1746662400/1746748800 - 15 Keys + 30 Refined

The Keys' histories in the 12 Key sale in your suggestion don't match. It looks more like the seller listed the item on Mannco.store. They might've instead sold it to someone who listed it there, but we can't know from the compare links, so that sale won't be usable.

With the 12 Key + 34 Refined sale in my comment being a quicksell, as well as the 13 Keys - 35 Refined sale, 12 can be excluded as a low outlier.

A range of 13 - 15 here would work.