SELECT 
  id_path 
FROM 
  cscart_categories 
WHERE 
  category_id IN (1531, 1618, 1808, 1834, 1902, 2002)

Query time 0.00038

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "p_category_id"],
      "key": "p_category_id",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "rows": 6,
      "filtered": 100,
      "index_condition": "cscart_categories.category_id in (1531,1618,1808,1834,1902,2002)"
    }
  }
}

Result