How to quickly scroll through a collection?

Question

.NET

Good afternoon. Please help to optimize the code with the following inputs:
- there is a grid, with about 10k records of my class;
- there is a collection that stores the selected records;
- there are two variables that return the sum of the elements in the selected records:

public virtual double TotalDebet => SelectedEntries.Sum(item => item.Debet);
        public virtual double TotalCredit => SelectedEntries.Sum(item => item.Credit);

- there is a code that updates these two variables:

protected void OnSelectedEntriesChanged()
        {
            this.RaisePropertyChanged(x => x.TotalCredit);
            this.RaisePropertyChanged(x => x.TotalDebet);
        }

The problem is this:
When selecting a large number of records (with the mouse or via Ctrl + A), the collection of selected objects is not instantly replenished, but gradually, respectively, and the amounts are calculated gradually, which greatly slows down the process. I would like to clarify how it is possible to implement either a delay, or something else so that the amount is considered only after a complete update of the collection.
Thank you.