The first thing that occurs is that the new committee can't change the levy – that can only be decided at a general meeting of the owners. Your strata managers should be on to that already (if they are any good).
Secondly, the Owners Corporation (that's all of you) has a legal responsibility to maintain common property. If they are not doing so and, in this case, it compromises the expected level of security for the building, they could face legal action at the CTTT.
And there is another element that might apply here (and I stress 'might'). If they have been warned that security has been dimished by their decision, and someone is huirt, robbed or has their property damaged by intruders, they MIGHT be guilty of culpable negligence which may not be covered by their insurance, leading to personal liability for EC members who voted against it. That may be a long shot but it's worth thinking about, just to get their attention.
Speaking generally, there are too many cases around of people buying bargain priced apartments (because of circumstances like yours) and rather than accepting the benefit already accrued, they try to reduce the building to a lower level of servic. It's not right and should be resisted.