Here is a code I tried to open a workbook and got the data:
Sub Open_Large_WB_ReadOnly()
    
    Dim WB As Workbook
    Dim WBdir As String
    Dim Start As Long
    
    Start = Timer
    
    WBdir = "C:... some very large workbook ... .xlsx"
    
    Set WB = Workbooks.Open(WBdir)
    Debug.Print WB.Sheets(1).Range("A1").Value
    WB.Close (False)
    
    Debug.Print " Regular " & Format(Timer - Start, "0.000")
    
End Sub
Timer total = Regular 38.066 -> 38 seconds is a long time.