Sale 1:

Sold for Purple Confetti Hound Dog (18.5) + 1 key

http://www.tf2outpost.com/trade/28821513 - No B/O

Seller: http://backpack.tf/profiles/76561198053252981#!/compare/1489708800/1489795200

Buyer: http://backpack.tf/profiles/76561198128550841#!/compare/1489622400/1489708800

X = 20

Sale 2:

Sold for Cool Minimal Wear Low Profile SMG (17)

No outpost

Seller: http://backpack.tf/profiles/76561198000247762#!/compare/1489708800/1489881600

Buyer: http://backpack.tf/profiles/76561198101293799#!/compare/1489795200/1489881600

SMG Suggestion (for ease of access): http://backpack.tf/suggestion/59306c4c0e2cad595d2b36f0

X = 17

Sale 3:

Sold for Cloud 9 Bombing Run (15)

http://www.tf2outpost.com/trade/28839796 - B/O of 16

Seller: http://backpack.tf/profiles/76561198284080404#!/compare/1489881600/1489968000

Buyer: http://backpack.tf/profiles/76561197974364849#!/compare/1488844800/1489968000

X = 15

Sale 4:

Quicksold for 13 keys + <0.5 keys in items

No outpost

Seller: http://backpack.tf/profiles/76561197974364849#!/compare/1488844800/1489968000

Buyer: http://backpack.tf/profiles/76561198213559089#!/compare/1489190400/1490054400

X = 13

Sale 5:

Sold for Orbiting Planets Samur-Eye

Seller: http://backpack.tf/profiles/76561198153088409#!/compare/1489622400/1489708800

Buyer: http://backpack.tf/profiles/76561198000247762#!/compare/1489622400/1489708800

Only sales I could find on the Samur-eye were bulk sales or quicksales. Can be used on the Samur-eye.

Sellers:

14.9 keys:

http://i.imgur.com/pmihUp8.png - 5 days, probably lowered/relisted

http://backpack.tf/item/294908452

http://backpack.tf/u/76561198304138933

Sales at:

13

15

17

20

13 quicksold, excluding 13.

20 looks like an outlier, and would also definitely be lower if we could access the B/O. Excluding 20.

Going with 15-17.