You'll need to add some proof showing that you valued this specific one at 16 and the other at 20 keys. Otherwise, this trade is bulky and shouldn't be used to price either hat, sorry.

Other sales:

Item 2: https://backpack.tf/item/16515353267

Sale 2:

https://backpack.tf/profiles/76561198093940897#!/compare/1766534400/1766793600

https://backpack.tf/profiles/76561198055923827#!/compare/1766707200/1766793600

15 keys

Sale 3:

https://backpack.tf/profiles/76561198055923827#!/compare/1768089600/1768348800

https://backpack.tf/profiles/76561198063640894#!/compare/1768262400/1768348800

Bulk for the North Star Mean Captain and Shrieking Shades Caribou Companion

Item 3: https://backpack.tf/item/16515335231

Sale 4:

https://backpack.tf/profiles/76561198093940897#!/compare/1766102400/1766361600

https://backpack.tf/profiles/76561199099768301#!/compare/1765324800/1766448000

Untrace

If the mods are fine with the confirmation you gave, I would go with 15-16 keys