CLOB column performance

I have a table in oracle DB with 3 columns:
CREATE TABLE MB_TRANSACTIONS(  
      NAME VARCHAR2(100) NOT NULL,
      CREATED_TS TIMESTAMP,
      MESSAGE CLOB NOT NULL
);
Inserts will be happened on this table through java Prepared statement:
<sql-definition>
      <sql>
            INSERT INTO ${PACKAGE}.MB_TRANSACTIONS(NAME,CREATED_TS, MESSAGE)
            VALUES(?,TO_DATE(?,'MM/DD/YYYY HH24:MI:SS'),?)
      </sql>
      <bindParams>
            <param seqNo="1" name="NAME" type="Types.VARCHAR"/>
            <param seqNo="2" name="CREATED_TS" type="Types.DATE"/>
            <param seqNo="3" name="MESSAGE" type="Types.CLOB"/>
      </bindParams>
</sql-definition>      
When the message size is large(7MB) PreparedStatement.execute() takes too long to Insert when  compared to smaller messages (1MB).
Large message time:
SQLStatement:execute() - Time took :31145ms
Smaller message:
SQLStatement:execute() - Time took :50ms

I am setting clob thru java code as follows:
 case Types.CLOB:
                   PreparedStatement cs;
                    if(value != null || !"".equals(value)){
                        cs.setObject(paramPosition, value);
                    }

My Questions:
1. Is there a way to improve the performance of the CLOB Fields ?
2. Do we need to consider any parameters on database while creating table with CLOB column.
3. Do I need to change any parameters on tablespace to make that fast?
4. Do I am doing Insertion in  a wrong way thru Java?