Improving Speed Comparing Multiple Columns

[David Hill]

I would like to please get assistance to improving speed for this particular following code because I have between 10,000 to 20,000 records.
In columns J and K are dates. In column L are integers.

Sub COMPAREMULTIPLECOLUMNS()

    Dim sh1 As Worksheet, sh2 As Worksheet

    Dim j As Long, i As Long, lastrow1 As Long, lastrow2 As Long

    Set sh1 = Worksheets("CURRENT")

    Set sh2 = Worksheets("PREVIOUS")

    

    lastrow1 = sh1.Cells(Rows.Count, "A").End(xlUp).Row

    lastrow2 = sh2.Cells(Rows.Count, "A").End(xlUp).Row

 

    For i = 2 To lastrow1

        For j = 2 To lastrow2

            If sh1.Cells(i, "F").Value = sh2.Cells(j, "F").Value Then

		If sh1.Cells(i, "J").Value <> sh2.Cells(j, "J").Value Then		

                sh1.Cells(i, "R").Value = sh2.Cells(j, "J").Value

            End If

	    End If

	    If sh1.Cells(i, "F").Value = sh2.Cells(j, "F").Value Then

		If sh1.Cells(i, "K").Value <> sh2.Cells(j, "K").Value Then		

                sh1.Cells(i, "S").Value = sh2.Cells(j, "K").Value

            End If
		
	    End If

	    If sh1.Cells(i, "F").Value = sh2.Cells(j, "F").Value Then

		If sh1.Cells(i, "L").Value <> sh2.Cells(j, "L").Value Then		

                sh1.Cells(i, "T").Value = sh2.Cells(j, "L").Value

            End If

            End If

        Next j

    Next i

End Sub

I would greatly appreciate any assistance.