Increasing starting time

The starting time of TWS is increasing.
The security is enabled on TWS. The URM is stored in a Tamino database. The authentication is done by Tamino.
The store in which the documents are managed is defined on the same database.

In my environment there is one acl by document in the store. I identified that the start time is linked to the number of the acl in the URM. TWS seems to load all acl in cache when it starts.
So more documents are loaded in the store more the starting time increases.

Is it a normal behavior?
Is there a way to reduce the starting time?
Can reduce the acl cache (defined in the urm_config.xml file) be a solution ?