Deferrender not working

Below is how I initialize the table. The table renders correctly with a hyperlink to the document but it loads a bit slow. I have around 4000 records and it takes around 3 secs. I want to add other columns to the table which I need to customize by render function as the below one. When I do that the render time increases to about 10 secsn which is not acceptable

I have a listener on rowCreated but it does not log anything. What am I doing wrong?

$('#listDocuments').DataTable({
"ajax" : {
'url' :'/WAS/admin/getDocumentsList',
'type' : 'GET',
'dataSrc':''
},
"destroy" : true,
"deferRender": true,
"autoWidth" : false,

    "columns": [
        {   
            'data': 'documentName',
            'defaultContent': 'documentName',
            'render': function (data, type, row, meta) {
                return generateHyperLink(row.documentName, row.documentLink);
            }
        }]

});