The optimization process and recommendations:

1. Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.

Optimal indexes for this query:

ALTER TABLE `aud_bat_t` ADD INDEX `aud_t_idx_tmp_id` (`tmp_id`);
ALTER TABLE `lg_clmn_t` ADD INDEX `lg_t_idx_lg_id` (`lg_col_id`);
ALTER TABLE `stats_dtl_t` ADD INDEX `stats_t_idx_batch_id` (`batch_id`);
ALTER TABLE `templ_t` ADD INDEX `templ_t_idx_tmplt_id` (`tmplt_id`);

The optimized query:

SELECT
        sb.col_nm + '.' + sb.col_r_nm AS 'Combined',
        mt.vlu_cd,
        at.tmplt_id 
    FROM
        templ_t at 
    INNER JOIN
        aud_bat_t b 
            ON b.tmp_id = at.tmp_id 
    INNER JOIN
        stats_dtl_t mt 
            ON mt.batch_id = b.batch_id 
    INNER JOIN
        lg_clmn_t sb 
            ON sb.lg_col_id = mt.lg_col_id 
    WHERE
        at.tmplt_id = 6 
    ORDER BY
        sb.col_nm + '.' + sb.col_r_nm,
        mt.vlu_cd,
        at.tmplt_id