I have tested the functionality of PreparedStatementCacheSize with Informix database, Its seems working fine without any issues. Have created a very simple test case to verify the functionality,
1. Created a Prepared statement.
2. Executed the statement in loop.
3. Closed the Prepared statement object.
4. Tried again using the prepared statement object to execute another loop, as this should be cached by the datasource connection when closing the object (in step3).
This confirms the functionality. Working as designed.