Column width is not working

debo

I have specified column width (15%) in 'columnDefs' as below, it's not forcing to pick up the specified width, it's taking width as per length of data. I have 'responsive' feature enabled and 'autoWidth' is set to false. Please let me know if I am doing it wrong.

"columnDefs": [{
    targets: getColumnIndexesWithClass( currentOptions.columns, "dt-position" ),
    "width" : "15%",
        render: function( data, type, full) {
        return '<div class="ellipsis">'+
                '<div style="overflow:hidden;white-space:nowrap;text-overflow:ellipsis;width:15%">'+
                    data +
                '</div>'
               '</div>';
    }
}],
"autoWidth": false,
"responsive": true