SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    21599, 21600, 21601, 21602, 21603, 21604, 
    21605, 21606, 21607, 21608, 21609, 
    21610, 21611, 21612, 21613, 21614
  )

Query time 0.00047

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 (21599,21600,21601,21602,21603,21604,21605,21606,21607,21608,21609,21610,21611,21612,21613,21614)"
    }
  }
}