Okay guys, 15-18 it is.

-Sold for 13 pure + strange peacenik(1 key) + ~10 ref in metal (taking 14 keys): http://backpack.tf/profiles/76561198137062595#!/compare/1482883200/1482969600

-B/O 17, not that it matters: http://www.tf2outpost.com/trade/28617589

-Quicksold for 10 pure: http://backpack.tf/profiles/76561198267189538#!/compare/1483574400/1483660800

-Sold for an OF pirate bandana(16 keys) + 3 keys (19 keys total): http://backpack.tf/profiles/76561198278073790#!/compare/1483747200/1483920000

-B/O 18.42 keys at the time, taking 18: http://www.tf2outpost.com/trade/28701481

-Untracable: http://backpack.tf/profiles/76561198149714284#!/compare/1486857600/1487376000 http://backpack.tf/item/4460727072

-Sold for 13 keys + 2 ref, taking 13: http://backpack.tf/profiles/76561198054047907#!/compare/1488153600/1488240000

-His B/O was 15: http://www.tf2outpost.com/trade/28805812

-Sold for 15 pure, credits to Mindacos: http://backpack.tf/profiles/76561198248485840#!/compare/1488240000/1488412800

-Bulk: http://backpack.tf/profiles/76561198093765664#!/compare/1488844800/1488931200

-B/O of 16 just in case: http://www.tf2outpost.com/trade/28809947

-Untracable: http://backpack.tf/profiles/76561198241616718#!/compare/1479859200/1489017600 http://backpack.tf/item/3626077918

-Sold for an aces airdog(14 keys) + 2 pure + 2 in sweets (18 keys total): http://backpack.tf/profiles/76561198114604882#!/compare/1484956800/1485129600

-B/O 20 just in case: http://www.tf2outpost.com/trade/28722447

-Added ~3 keys in sweets for a CPS hotrod(15.5, taking 16 keys) (13 keys total): http://backpack.tf/profiles/76561198070722832#!/compare/1485302400/1485388800

-???: http://backpack.tf/profiles/76561198054270952#!/compare/1484870400/1484956800

-Sold w/ ~ 2 keys in sweets for an OF tree(18.5, taking 19 keys) (17 keys total): http://backpack.tf/profiles/76561198162607083#!/compare/1488326400/1488412800

Taking 15-18 thanks to the sales above.