The optimization process and recommendations:

1. Avoid Selecting Unnecessary Columns (query line: 2): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
2. 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:

CREATE INDEX larticles_idx_id ON LARTICLES (ID);
CREATE INDEX lcadep_idx_id ON LCADEP (ID);
CREATE INDEX lmaterial_idx_id ON LMATERIAL (id);
CREATE INDEX torder_cmk_idx_id ON TORDER_CMK (ID);
CREATE INDEX tporder_cmk_idx_plan_id ON tporder_cmk (PLAN_ID);

The optimized query:

SELECT
        tp.*,
        la.*,
        lm.*,
        ld.*,
        ld1.*,
        to_cmk.* 
    FROM
        ppu_plan.tporder_cmk tp 
    JOIN
        PPU_PLAN.LARTICLES la 
            ON TP.ARTICLE = LA.ID 
    JOIN
        PPU_PLAN.LMATERIAL lm 
            ON TP.MATERIAL = lm.id 
    JOIN
        PPU_PLAN.LCADEP ld 
            ON TP.CADEP = LD.ID 
    JOIN
        PPU_PLAN.LCADEP ld1 
            ON TP.PRODUCER = LD1.ID 
    JOIN
        PPU_PLAN.TORDER_CMK to_cmk 
            ON TP.order_id = TO_cmk.ID 
    WHERE
        TP.PLAN_ID = :pplan_id