SELECT 
  category_id, 
  parent_id 
FROM 
  categories 
WHERE 
  parent_id IN(
    7728, 8457, 7108, 7109, 8324, 8323, 7731, 
    7730, 7729, 7734, 7733, 7726, 7732, 
    7727, 7725
  )

Query time 0.00057

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "3.71"
    },
    "table": {
      "table_name": "categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 15,
      "rows_produced_per_join": 15,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "2.21",
        "eval_cost": "1.50",
        "prefix_cost": "3.71",
        "data_read_per_join": "39K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`goimagine`.`categories`.`parent_id` in (7728,8457,7108,7109,8324,8323,7731,7730,7729,7734,7733,7726,7732,7727,7725))"
    }
  }
}