SELECT 
  category_id, 
  parent_id 
FROM 
  categories 
WHERE 
  parent_id IN(
    15805, 15580, 15634, 15581, 15633, 16218, 
    15636, 16033, 15616, 15579, 15635, 
    15593, 15586, 15589, 15587, 16111, 
    15592, 15582, 15585, 15588, 15590, 
    15578, 15584, 15591, 15594
  )

Query time 0.00079

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "9.25"
    },
    "table": {
      "table_name": "categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 43,
      "rows_produced_per_join": 43,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "4.95",
        "eval_cost": "4.30",
        "prefix_cost": "9.25",
        "data_read_per_join": "112K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`goimagine`.`categories`.`parent_id` in (15805,15580,15634,15581,15633,16218,15636,16033,15616,15579,15635,15593,15586,15589,15587,16111,15592,15582,15585,15588,15590,15578,15584,15591,15594))"
    }
  }
}