Hi,
unfortunately, I don’t really have ideas on this one.
At first, you should try to find out where the delay comes from. Is it the loading of the actual content (HTML file) or the execution of the JavaScript library?
To test that, please temporarily deactivate the usage of the DataTables library for your table and (after clearing your browser cache again), load the page again. If the delay is still there, the problem might indeed be the size of the table in WP-Table Reloaded. In that case, switching to a custom mySQL/PHP solution might help. I don’t have tutorials for this, but anything about PHP/mySQL interaction should be a good starting point.
If the delay vanishes after deactivating the usage of the JS library, the problem basically is the usage of that library. You will then have to either accept the delay or stop using the library…
Regards,
Tobias