Slow and steady wins the race.

https://backpack.tf/item/2834653145

Sale 1) Sold for a Green Confetti Big Chief (16 Keys)

https://backpack.tf/profiles/76561198097381339#!/compare/1545868800/1546041600

Big Chief Mini

https://backpack.tf/suggestion/5c441b99cf6c75280c5c4336 - 16 Keys

Sale 2) Sold for a Circling TF Logo Engineer's Cap (15.5 Keys)

https://backpack.tf/profiles/76561198097381339#!/compare/1546128000/1546214400

Rounds to 16 Keys

Engineer's Cap Mini

https://backpack.tf/suggestion/5c48a41e44325a726b30b9dd - 15.5 Keys

Sale 3) Sold for 15 Keys + 1.22 Refined to a buy order

https://backpack.tf/profiles/76561198260467278#!/compare/1546214400/1546300800

Low outlier.

https://marketplace.tf/items/30314;5;u60 - Sold for $25.55 when Keys were ~$1.79 each

https://marketplace.tf/items/5021;6/Mann%20Co.%20Supply%20Crate%20Key

25.55 / 1.79 = 14.27 Keys

Low outlier.