SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (
    1, 16, 19, 27, 38, 46, 61, 83, 117, 235, 
    236, 257, 261, 304, 306
  )

Query time 0.00033

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "rows": 15,
      "filtered": 100,
      "index_condition": "cscart_categories.category_id in (1,16,19,27,38,46,61,83,117,235,236,257,261,304,306)"
    }
  }
}