Copy and Paste Special (Transpose) multiple times

In my worksheet I have 15 columns of data in 60 rows, each row's 15 data inputs represent a single scenario.

I want to copy the data in each row, transpose it to a separate input field, which will then calculate an output to a cell next to the input row in column P. Is this the most efficient way?

Sub Final()
Dim Cell_Reference As Range

Set Cell_Reference = Range("P" & Rows.Count).End(xlUp).Offset(1)

Range(Cell_Reference.Offset(, -15), Cell_Reference.Offset(, -1)).Copy
Range("R4").PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=True
Range("R20").Copy
Range("P" & Rows.Count).End(xlUp).Offset(1).Select
Selection.PasteSpecial xlPasteValues
Range("R4:R18").Select
Selection.ClearContents

End Sub

This second code is an attempt to bypass doing a loop and running the first macro for each row of inputs. There has to be a better way to do this.

Sub Run_Final()
'
' Macro2 Macro
'

'
    Application.Run "'G&I WIP ULTRA - Copy - Copy.xlsm'!Final"
    Application.Run "'G&I WIP ULTRA - Copy - Copy.xlsm'!Final"
    ' and 55 times more
End Sub

Get output for each scenario with a For loop.

btw, it's helpful to read:

How to avoid using Select in Excel VBA

Microsoft documentation:

Range.Resize property (Excel)

Sub Final()
    Dim Cell_Reference As Range
    Dim lastRowP As Long, lastRowA As Long, i As Long, aRes()
    ' get the last row# on col A and P
    lastRowP = Range("P" & Rows.Count).End(xlUp).Row
    lastRowA = Range("A" & Rows.Count).End(xlUp).Row
    If lastRowA <= lastRowP Then Exit Sub
    ' declare an array to store output on col P
    ReDim aRes(1 To lastRowA - lastRowP, 0)
    ' loop through each row
    For i = lastRowP + 1 To lastRowA
        ' update scenario input on col R
        Range("R4").Resize(15, 1).Value = Application.Transpose(Cells(i, 1).Resize(1, 15).Value)
        ' store the output
        aRes(i - lastRowP, 0) = Range("R20").Value
    Next
    ' write output to sheet
    Cells(lastRowP + 1, "P").Resize(lastRowA - lastRowP, 1).Value = aRes
    Range("R4").Resize(15, 1).ClearContents
End Sub