SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    20701, 20702, 20703, 20704, 20705, 20706, 
    20707, 20708, 20709, 20710, 20711, 
    20712, 20713, 20714, 20715, 20716
  )

Query time 0.00030

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 (20701,20702,20703,20704,20705,20706,20707,20708,20709,20710,20711,20712,20713,20714,20715,20716)"
    }
  }
}