SAP PO 7.4 Synchronous messages

Hi, we are inSAP PO java stack , we have an synchronous interface which has 3million traffic per day. Front end -->Middleware-->SAP PI-->SAP OER-->SAP HANA.Lot of times Front end and Middleware complain of high response time for few minutes, and I can also see high response times in SAP PI performance monitoring but we are not sure where the delay is happening. I guess delay is in down stream OER or HANA. How to troubleshoot this issue. Is there any other way to check in PI as it will not be possible to check synchronous messages with this high volume in that particular time in message monitoring.Thank you.