The optimization process and recommendations:

1. Avoid Subqueries (query line: 8): We advise against using subqueries as they are not optimized well by the optimizer. Therefore, it's recommended to join a newly created temporary table that holds the data, which also includes the relevant search index.
2. Avoid Subqueries (query line: 16): We advise against using subqueries as they are not optimized well by the optimizer. Therefore, it's recommended to join a newly created temporary table that holds the data, which also includes the relevant search index.
3. 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 test_event_idx_event_id ON "test_event" ("event_id");
CREATE INDEX test_table_idx_sequence_id_test_id ON "test_table" ("sequence_id","test_id");

The optimized query:

SELECT
        test_table.value1,
        test_table.value2 
    FROM
        test_table 
    WHERE
        test_table.sequence_id IN (
            SELECT
                test_event.sequence_id 
            FROM
                test_event 
            WHERE
                test_event.event_id = 1
        ) 
        AND test_table.test_id IN (
            SELECT
                test_event.test_id 
            FROM
                test_event 
            WHERE
                test_event.event_id = 1
        )