If the CTE date is 6/15 I can't imagine there will be movement in August unless, as
@wysdoc suggested, someone gets cold feet or has some sort of emergency, since it is EXTREMELY unlikely any school would call someone who is CTE elsewhere off a WL.
The bad news for you is that this will prevent people currently PTE there from accepting last minute WL offers elsewhere. The good news is that you will have virtual certainty where you stand by the end of June, regardless of what you've heard about August movement. Do you happen to know whether they had a later CTE date the last two years?
WL movement several weeks after a CTE date is quite rare. On the other hand, having a CTE date that much before classes begin is also not common, so, who knows?