It may be necessary to set additional LDAP provider properties (see the Oracle documentation for a full list) in order to ensure optimum performance. Two specific values you should consider setting are:

com.sun.jndi.ldap.connect.timeout

The value is the number of milliseconds to use as the connection timeout.
Note: As of version 1.48 of the AD plugin this value has a default, if not set, of 30 seconds.

com.sun.jndi.ldap.read.timeout

The value is the number of milliseconds to use as the read timeout.
Note: As of version 1.48 of the AD plugin this value has a default, if not set, of 60 seconds