SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.meta_keywords, 
  cscart_product_descriptions.meta_description, 
  cscart_product_descriptions.search_words, 
  cscart_product_descriptions.promo_text, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    9984, 9985, 9986, 9987, 9988, 9989, 9990, 
    9991, 9993, 9994, 9995, 9996, 9997, 
    9998, 9999
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 15,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (9984,9985,9986,9987,9988,9989,9990,9991,9993,9994,9995,9996,9997,9998,9999) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}