also try doing ssh -v <hostname> and see if the output throws any exceptions..
check the root dir for the .ssh dir (hidden file). check the known_hosts file if the servers' key which you're trying to ssh from is planted. Sorry bro, I wish I could help my level best, but without me trying infront of the system its always hard for me to put into good words...

In all other servers the gateway is 10.15.14.1

Did you create a password for the user using "passwd" at your destination host?. Even though you copied the public key correctly, and a match was found, the ssh daemon might throw an error that it failed public key authorization, and client would wait at a password prompt.
Fyi

is it a /etc/netmask or /etc/defaultrouter problem then?

yeah i can do ssh with ip, Its working

while doing nslookup it does not return to server ip
and sshd_config is not there and no ssh directory in etc.

the defaultrouter and netmasks is different in both servers. will it could be a problem.

what i need to do now, need to change the netmasks and defaultrouter as the prod server