Memory Consumption in Requests

I have a question about memory consumption when receiving a frontend request, for example.

In this first example, let’s suppose that the user created an order

"order": {
  "order_code": "123",
  "items": [
    {
      name: "item name 1",
      quantity: 1,
      price: 100.0
    },
    {
      name: "item name 2",
      quantity: 2,
      price: 100.0
    },
    {
      name: "item name 3",
      quantity: 3,
      price: 100.0
    }
  ]
}

And each item should have the same “order_code” too, for some logic business.
In the backend, we should map each item and copy the order_code inside it.

In this second example, the frontend is responsible for sending the order_code for each item and the backend should validate if the order_code in each item is equal to the order’s order_code.
(The customer don’t need to see this field as long as the frontend send as a “hidden” input, for example)

"order": {
  "order_code": "123",
  "items": [
    {
      name: "item name 1",
      quantity: 1,
      price: 100.0,
      order_code: "123"
    },
    {
      name: "item name 2",
      quantity: 2,
      price: 100.0,
      order_code: "123"
    },
    {
      name: "item name 3",
      quantity: 3,
      price: 100.0,
      order_code: "123"
    }
  ]
}

Creating some test using Grafana and Prometheus, I had some results where the request duration in milliseconds was higher in the first example than the second.

But, using erlang.memory(:total) the second example was consuming more memory than the first example for some reason.

I thought that in the first example the memory consumption would be greater, as another data is created in memory for the new items with order_code.

How does memory consumption work in this case?
Is it advisable to do this type of mapping in Backend or should we just validate the data?