ok, If you have the scene saved , load it into poser, open the keyframe editor , and drag the selection box around all the keyframes at frame 30. Then press the delete key.

You dont need any keyframes after your pose at frame 15 if you just want the cloth sim to run past it .
If its messed up then apply your pose at frame 15 and try again .     :)

I normally run cloth sims over 40-60 frames and have the pose at frame 20 or even 30 depending on what I am doing . There should be enough frames that the cloth hangs without moving during the last few frames of the sim .

You can use "steps per frame"  if you are trying to fit cloth in an animation .