Try it as below instead:
​Sub test()
    Dim fDay As Variant, endRow As Long
    
    fDay = DateSerial(Year(Date), Month(Date), 1)
    endRow = Range("O" & Rows.Count).End(xlUp).Row
    
    Range("O7").AutoFilter Field:=15, Criteria1:="<" & CLng(fDay)
    On Error Resume Next
    Range("8:" & endRow).SpecialCells(xlCellTypeVisible).Delete
    On Error GoTo 0
    Range("O7").AutoFilter Field:=15

End Sub