Need help to reduce the execution time for the code below - excel

Question

Below code compares 1500 rows with about 14 columns . It takes around 30 min to execute them . Is there any way , I could reduce the code by altering the code below .I like to get all your expert opinion.
The code makes the following function
Run through all records in Old Sheet.
if found in NEW sheet , Do nothing
if not found in NEW sheet , Delete it from OLD sheet
Option Explicit
Function UpdateOLD() As Long
' This Sub will do the Following Update
' Run through all records in OLD
' if found in NEW ---> Do nothing
' if not found in NEW ----> Delete it from OLD.
'
Dim WSO As Worksheet
Dim WSN As Worksheet
Dim MaxRowO As Long, MaxRowN As Long, I As Long, J As Long, lDel As Long
Dim sJob As String, sOps As String, sFirstAddress As String
Dim cCell As Range
Dim bNotFound As Boolean
'---> Disable Events
With Application
.EnableEvents = False
.DisplayAlerts = False
.ScreenUpdating = False
End With
'---> Set Variables
Set WSO = Sheets("Steps")
Set WSN = Sheets("Interface")
MaxRowO = WSO.Range("A" & WSO.Rows.Count).End(xlUp).Row
MaxRowN = WSN.Range("C" & WSN.Rows.Count).End(xlUp).Row
WSO.Range("N2:N" & MaxRowO).ClearContents
'---> Loop thruough all rows in sheet New
For I = MaxRowO To 2 Step -1
bNotFound = False
sJob = WSO.Cells(I, "B")
sOps = WSO.Cells(I, "C")
Set cCell = WSN.Range("D6:D" & MaxRowN).Find(what:=sJob, LookIn:=xlValues, lookat:=xlWhole, MatchCase:=False)
If Not cCell Is Nothing Then
bNotFound = True
sFirstAddress = cCell.Address
Do
'---> Check to See if Ops if found for that Job
If WSN.Cells(cCell.Row, "E") = sOps Then
bNotFound = False
Exit Do
End If
Set cCell = WSN.Range("D6:D" & MaxRowN).FindNext(cCell)
Loop While Not cCell Is Nothing And cCell.Address <> sFirstAddress
Else
bNotFound = True
End If
'---> Del Record from OLD if Not Found
If bNotFound Then
WSO.Range(I & ":" & I).EntireRow.Delete
'WSO.Range("N" & I) = sJob & " " & sOps & " Deleted as NOT found in NEW"
lDel = lDel + 1
End If
Next I
'---> Enable Events
With Application
.EnableEvents = True
.DisplayAlerts = True
.ScreenUpdating = True
End With
UpdateOLD = lDel
End Function

Answer 1

Welcome to SO.Tried your code with around 2000 rows with around 10% mismatch and it take only few seconds. may be the file have some other issues. However one way to speed up (about 1/2 the time taken in my trial) is to add all the bNotFound cells in a union of range and delete the EntireRow of the range in one shot after finishing the loop.
Changes in Code:
Dim Rng As Range 'Add in Declare section
'
'
'
'
For I = 2 To MaxRowO 'No need to loop backward
'
'
'
'
If bNotFound Then ' Only add to Union of ranges
If Rng Is Nothing Then
Set Rng = WSO.Range("A" & I)
Else
Set Rng = Union(Rng, WSO.Range("A" & I))
lDel = lDel + 1
End If
End If
Next I
If Not Rng Is Nothing Then Rng.EntireRow.Delete ' delete in one shot