SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21567, 21568, 21569, 21570, 21571, 21572, 
    21573, 21574, 21575, 21576, 21577, 
    21578, 21579, 21580, 21581, 21582
  )

Query time 0.00036

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 (21567,21568,21569,21570,21571,21572,21573,21574,21575,21576,21577,21578,21579,21580,21581,21582)"
    }
  }
}