Hi Deepak,
Have you analysed the message processing logs to see where the delay is in the call? Such as, message mapping, calling the receiver system etc.
Also, have you looked at the performance monitoring analysis to get more insight on issue?
Unless the performance issue is caused in SAP PI system (bad mapping design etc.), you can't do much on SAP PI side. If the issue is not in SAP PI system, try to identify if it is being caused because of network latency or end system side.
Regards,
Sanjeev.