Hello Sathish
There may be several reasons for an OSPF neighbor adjacency to be stuck in the Exstart or Exchange states. One of those is indeed the MTU size. Since you have identified this as the problem, and you have confirmed that the size of the pings that are able to go through are 8096 bytes, then this must be the reason.
Now why are your pings not going through at the expected maximum MTU of 9216? Like you said, this is likely the maximum MTU that is allowed on the intervening infrastructure between the routers. What do you have between those two OSPF routers? Are the connected with a single cable or are they communicating over another network infrastructure?
Let us know so that we can help you further.
I hope this has been helpful!
Laz