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 (
    15943, 15951, 15952, 15956, 15958, 15959, 
    15944, 15960, 15961, 15962, 15966, 
    15957, 15965, 15945, 15968, 15946, 
    15947, 15950
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00225

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": 18,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (15943,15951,15952,15956,15958,15959,15944,15960,15961,15962,15966,15957,15965,15945,15968,15946,15947,15950) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}