SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (
    6, 15, 16, 17, 18, 61, 62, 67, 68, 73, 82, 
    83, 206, 233, 234, 235, 236, 237, 238, 
    242, 264, 306, 336
  )

Query time 0.00041

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": 23,
      "filtered": 100,
      "index_condition": "cscart_categories.category_id in (6,15,16,17,18,61,62,67,68,73,82,83,206,233,234,235,236,237,238,242,264,306,336)"
    }
  }
}