SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21759, 21760, 21761, 21762, 21763, 21764, 
    21765, 21766, 21767, 21768, 21769, 
    21770, 21771, 21772, 21773, 21774
  )

Query time 0.00031

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 (21759,21760,21761,21762,21763,21764,21765,21766,21767,21768,21769,21770,21771,21772,21773,21774)"
    }
  }
}