SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21775, 21776, 21777, 21778, 21779, 21780, 
    21781, 21782, 21783, 21784, 21785, 
    21786, 21787, 21788, 21789, 21790
  )

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 (21775,21776,21777,21778,21779,21780,21781,21782,21783,21784,21785,21786,21787,21788,21789,21790)"
    }
  }
}