SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    4135, 4814, 4845, 4846, 4844, 4848, 4847, 
    4849, 4843, 4842, 4850, 4855, 4851, 
    4853, 4852, 4854
  )

Query time 0.00035

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (4135,4814,4845,4846,4844,4848,4847,4849,4843,4842,4850,4855,4851,4853,4852,4854)"
    }
  }
}