This is how to get the “We Cannot Linger” achievement easily.
We Cannot Linger Achievement Guide
So basically there’s a glitch that you can do. Once you get to the part where you are at the staircase, save the game using the statue in the image. You can now exit the level, and then come back, and the timer will restart. The last part isn’t too hard, as long as you finish it before 15 minutes.