Two recent marketplace.tf sales in the latest months;

https://marketplace.tf/items/tf2/1107;5;u3097

One sale on July 14th at $24.99 / $1.69 = 14.79 keys, rounding to 15, outlier

One sale on July 22nd at $24.99 / $1.7 = 14.80 keys, rounding to 15, outlier

One sale on October 10th at $24.99 / 1.9 = 13.15 keys, rounding to 13 keys.

https://backpack.tf/item/7842416305

https://backpack.tf/profiles/76561198054270952#!/compare/1724716800/1724803200

https://backpack.tf/profiles/76561199508870360#!/compare/1724284800/1724803200

sold for 13 keys (thank you bentry suster for the find)

https://backpack.tf/profiles/76561199026390261#!/compare/1721520000/1721606400

https://backpack.tf/profiles/76561199042384821#!/compare/1721260800/1721606400

sold with ~45 ref for Potion Explosion Taunt: Soldier's Requiem + Sublime Snowstorm Taunt: Flippin' Awesome

https://marketplace.tf/items/tf2/1107;5;u3087 - recent sale at 14.99 / 1.7 = 8.8, rounding to 9.

https://marketplace.tf/items/tf2/30673;5;u3128 - recent sale at 9.99 / 1.7 = 5.8, rounding to 6.

Based on recent sales, ~14 is another outlier

Rest of the sales are untraceable.

Classifieds has unsolds at 11

Taking 11 to 13