SELECT 
  product_id, 
  amount 
FROM 
  cscart_warehouses_destination_products_amount 
WHERE 
  product_id IN (
    6470, 5590, 5591, 5650, 6471, 6849, 5651, 
    6751, 6838, 6839, 6777, 6778, 6472, 
    5649, 5648, 5647
  ) 
  AND destination_id = 115 
  AND storefront_id = 0

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_warehouses_destination_products_amount",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "idx_storefront_id"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "destination_id", "storefront_id"],
      "rows": 16,
      "filtered": 75,
      "index_condition": "cscart_warehouses_destination_products_amount.destination_id = 115 and cscart_warehouses_destination_products_amount.storefront_id = 0 and cscart_warehouses_destination_products_amount.product_id in (6470,5590,5591,5650,6471,6849,5651,6751,6838,6839,6777,6778,6472,5649,5648,5647)"
    }
  }
}