Sale 1:

Sold for Smoking Milkman (14) + 1 key + <0.5 keys in metal/items

No outpost

Seller: http://backpack.tf/profiles/76561198148843171#!/compare/1490400000/1490486400

Buyer: http://backpack.tf/profiles/76561198320285393#!/compare/1490400000/1490486400

X = 15

Sale 2:

Sold with Pro. KS Strange Festive Revolver (3) for Spec. KS Aussie Knife (17)

No outpost

Seller: http://backpack.tf/profiles/76561198199309913#!/compare/1489708800/1489795200

Buyer: http://backpack.tf/profiles/76561198072715791#!/compare/1482883200/1491264000

X = 14

Sale 3:

Sold for Magnetic Hat Protector Head Full of Hot Air (12) + 2 keys

No outpost

Seller: http://backpack.tf/profiles/76561198084572340#!/compare/1490140800/1490227200

Buyer: http://backpack.tf/profiles/76561198148843171#!/compare/1490140800/1490227200

X = 14

Sale 4:

Sold for Logo Puffy Provocatuer

Seller: http://backpack.tf/profiles/76561198110011480#!/compare/1489708800/1489795200

Buyer: http://backpack.tf/profiles/76561198199309913#!/compare/1489708800/1489795200

Can be used to update the Provocateur

Sellers:

14.5 keys:

http://i.imgur.com/2cuclfI.png - 4 days, probably re-listed.

http://backpack.tf/u/76561198337734785

18 keys:

http://i.imgur.com/CHLRp3S.png - 1 day

http://backpack.tf/u/76561198004236703

19 keys:

http://i.imgur.com/gmEe5IE.png - 8 days

http://backpack.tf/u/76561198024766381

20 keys:

http://i.imgur.com/IWZzthr.png - 2 months

http://backpack.tf/u/76561198316071886

$43.25: (~20.5 keys)

https://backpack.tf/item/2674926324

https://marketplace.tf/items/100;5;u60

Sales at:

14 (2x)

15

Going with 14-15.