SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    20637, 20638, 20639, 20640, 20641, 20642, 
    20643, 20644, 20645, 20646, 20647, 
    20648, 20649, 20650, 20651, 20652
  )

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 (20637,20638,20639,20640,20641,20642,20643,20644,20645,20646,20647,20648,20649,20650,20651,20652)"
    }
  }
}