[Dovecot] LDAP: Connection lost to LDAP server, reconnecting

Hi! Sorry by my english. Set Postfix + dovecot + AD + ldap, everything works well, but appears in the logs, every 15 minutes:

auth(default): Error: LDAP: Connection lost to LDAP server, reconnecting

Standart limit ldap connect to AD 15 minutes. Can somehow fix this problem without increasing the time of connection to the AD?