SQL Query to display minimum prices per country
try {
            Connection con = Mycon.getConnection();



This probably could be 

    try (Connection con = Mycon.getConnection()) {


Assuming that this is the Java.sql.Connection interface.  

Then the try-with-resources would be able to close the connection for you--exception or no exception.  

But that won't help with your speed issues.  

You need to determine where the problem lies.  Is it the query at the end?  Is it the population of the table?  The creation of the jTable?  Where?  

Are there any conid values in venprices that aren't in country?  It would seem that there would have to be, as there are only 30,000 records in country and 180,000 in tempcalcplan.  Both have conid as their primary key, so no duplicates.  

Is there an index on conid and rate in venprices?