Opening Excel files and using cell values in formulas

Hello,

I'm creating an Excel file which lets the user choose if he wants the data with or without management override. The problem is that the data in the summary depend on 14 Excel files, so I have to open them all. So in the macro, I need to

1. Open all the Excel files
2. If Management Override is set to "W", set it to "W" in the 14 files. If it is set to "W/O", set it to "W/O".
3. Put the good values in the cells with .Formula="..."

I'm using something like this :

Sub Bouton1_Clic()
    
    Application.ScreenUpdating = False
    Workbooks.Open Filename:=" .....
    
    If Range("E5") = "W" Then
        
        Workbooks("MTP 2009-2012 Ontario Broker.xlsm").Worksheets("UW Income").Range("C4").Value = "W"
.....
        Range("C12").Formula = "='H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Broker.xlsm]UW income'!P13+'H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Commercial.xlsm]UW income'!Q13+'H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Novex.xlsm]UW income'!Q13"
        Range("C12:C18").FillDown
        Range("C22").Formula = "=(('H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Broker.xlsm]UW income'!P23*'H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Broker.xlsm]UW income'!P13)+('H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Commercial.xlsm]UW income'!Q23*'H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Commercial.xlsm]UW income'!Q13)+('H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Novex.xlsm]UW income'!Q23*'H:\Corporate\MTP\work\Ontario\[MTP 2009-2012 Ontario Novex.xlsm]UW income'!Q13))/C12"
        Range("C22:C28").FillDown
etc.

The problem is that it is very long to load (about 2 min for the entire macro). Is there a way to run it faster?

Thanks