[Exim] Time too long

When i send a message from 192.168.1.137 (myPC on LAN) to 213.188.254.254
(Exim SMTP server on WAN) i have to wait 15 second before it starts to send
my mail.
I've tried with a telnet on port 25, i have to wait 15 second before it
respond:

220 myhost.mydomain.it ESMTP Exim 3.13 #1 Wed, 05 Jul 2000 14:24:16 +0200

In debug mode i see this:
When i try to connect:
Connection request from 192.168.1.137
and after 15 seconds:
Process 20541 is handling incoming connection from [192.168.1.137]
ready for new message

This problem happens only when i send e-mail from my LAN.

Thank you.