This is one of the harder level to speedrun, even on easy difficulty. Below is a guide for speedrunning this level on legendary courtesy of Nak3dEli and ProAceJoker. Follow this guide an you should have no problem getting this achievement on any difficulty. ProAceJoker did it in about 15:30, You have about 9 minutes for errors, the par time is 25 minutes. Also you can use the save/quit method to set your time back to the point you were at when you originaly hit a checkpoint, but does not work on the last checkpoint of the level.