Sales supporting the range:

Both sales are very confusing, as there appears to be a hole in the item's history on both Outpost and Backpack

Sale 1:

Sold for 13 keys + Capper

No outpost link available

Seller: http://backpack.tf/profiles/76561197975641533/#!/compare/1453017600/1454659200

The buyer in this sale does not support the sale at all, instead, I'm going to link the items that were involved:

http://www.tf2outpost.com/item/440,4490327438

http://www.tf2outpost.com/item/440,4490327439

http://www.tf2outpost.com/item/440,4490327441

http://www.tf2outpost.com/item/440,4490327442

http://www.tf2outpost.com/item/440,4490327443

http://www.tf2outpost.com/item/440,4490327444

http://www.tf2outpost.com/item/440,4490327445

http://www.tf2outpost.com/item/440,4490327446

http://www.tf2outpost.com/item/440,4490327447

http://www.tf2outpost.com/item/440,4490327448

http://www.tf2outpost.com/item/440,4490327449

http://www.tf2outpost.com/item/440,4490327450

http://www.tf2outpost.com/item/440,4490327451

http://www.tf2outpost.com/item/440,4345365969 (Capper)

Buyer's profile: http://backpack.tf/profiles/76561198183429249

X = 13 + 2

X = 15

Sale 2:

Sold for 15 keys

Buyer: http://backpack.tf/profiles/76561197989384192/#!/compare/1452499200/1452672000

Similar issue to sale 1, going to link all items that were involved in the trade

http://www.tf2outpost.com/item/440,4517520307

http://www.tf2outpost.com/item/440,4165898257

http://www.tf2outpost.com/item/440,4498042026

http://www.tf2outpost.com/item/440,4620628626

http://www.tf2outpost.com/item/440,4498041985

http://www.tf2outpost.com/item/440,4498042042

http://www.tf2outpost.com/item/440,4498042051

http://www.tf2outpost.com/item/440,4571045546

http://www.tf2outpost.com/item/440,4498042062

http://www.tf2outpost.com/item/440,4498042072

http://www.tf2outpost.com/item/440,4498042076

http://www.tf2outpost.com/item/440,4498042089

http://www.tf2outpost.com/item/440,4498042098

http://www.tf2outpost.com/item/440,4498042002

http://www.tf2outpost.com/item/440,4597969568

X = 15

The sales happened in this order:

Ishamon --> Darude Dankstorm --> Ninja Scout

http://backpack.tf/profiles/76561197989384192 --> http://backpack.tf/profiles/76561198183429249 --> http://backpack.tf/profiles/76561197975641533

Sellers:

16 keys:

http://puu.sh/nqFuh/4ff4a8d7ca.png - 3X, 1 listed 10 days ago, 1 listed 14 days ago, 1 listed recently

Two sales at 15 keys

Going with 15 keys