This is by far my most researched suggestion.

10 months old price.

It's almost impossible too sell at the current range. I'm putting a range of 15-17 keys because of one sale at 17-19 keys, one at 17 and 2 around 15.

Unsolds:

http://backpack.tf/classifieds/search/id/52e36c334cd7b8cf288b4567 - 22 keys, 4 days

http://www.tf2outpost.com/trade/19425404 - 21 keys, 1 week (1.1)

http://www.tf2outpost.com/trade/19669824 - 24 keys, 19 hours (Young) (~1.3)

http://www.tf2outpost.com/trade/19616100 - 21 keys, 3 days (1.1)

Solds:

http://www.tf2outpost.com/trade/19598145 - 17 keys

http://backpack.tf/profiles/76561198037130446?time=1399100400 > http://backpack.tf/profiles/76561198037130446?time=1399186800

http://www.tf2outpost.com/trade/19591388 - 15 keys + 3 ref

http://backpack.tf/profiles/76561198127032480?time=1398841200 > http://backpack.tf/profiles/76561198127032480?time=1398927600

http://www.tf2outpost.com/trade/19496239 - 16 keys

http://www.tf2outpost.com/trade/19450288 - 2 buds for drill + o.f safe'n'sound (Valued ~1-1.1 bud). So basically 17-19 keys

http://www.tf2outpost.com/trade/18925332 - 15 keys

http://backpack.tf/profiles/76561197999824441?time=1397890800 > http://backpack.tf/profiles/76561197999824441?time=1397977200

That should be enough too set a new range.