A GMAT plateau can certainly happen, but I would be careful about treating it as something that simply happens to everyone and that you need to wait out.
A drop from around 615 to 575 is information. Something has changed, and your job is to figure out what.
First, determine whether the 615 was truly representative. Was it a fresh official practice test taken under realistic conditions, or had you seen some of the questions before? Were both tests taken under comparable conditions?
Assuming the scores are legitimate, I would look closely at the section-level performance and, more importantly, at the questions you missed.
Ask yourself:
Did your accuracy decline in certain topics?
Did you spend too much time on a few difficult questions and then rush later?
Are you making more careless mistakes?
Are you struggling with questions you previously handled comfortably?
Has fatigue or anxiety started affecting your execution?
Have you shifted too heavily toward timed practice and away from actually improving weak areas?
One of the biggest mistakes people make when they believe they have plateaued is simply doing more questions and more mock tests. If there are underlying knowledge or skill gaps, repeatedly testing yourself does not fix them.
Go back to the areas that are costing you points and rebuild them carefully. Study the concepts, review your approaches, and do focused practice until your accuracy becomes consistently high. Then layer timing back in.
Also, don't allow a few disappointing scores to destroy your confidence. GMAT performance can fluctuate. A 575 does not suddenly erase the knowledge and skills that allowed you to score 615.
But I also would not dismiss the decline as random. Diagnose it.
A plateau is not a diagnosis. It is a symptom.
Figure out what is preventing your score from moving forward, fix that specific issue, and the score can start moving again.
Good luck!
- Scott, TTP