How to stop Macro from looping

Hello all,

I have a macro code that automatically saves after every 15 minutes. however, after closing the sheet (not excel) and opening a new program. It opens the program with the macro that saves every 15 minutes without me trying to open it.

Here's the code in ThisWorkbook

Private Sub Workbook_Open()
Application.OnTime Now + TimeValue("00:15:00"), "saveIt"
End Sub

Code in Modules

Module 1

Sub saveIt()
    Application.DisplayAlerts = False
    ActiveWorkbook.SaveAs Filename:=ActiveWorkbook.FullName, FileFormat:=xlNormal
    Call UpdateTime
End Sub

Module 2

Sub UpdateTime()
    Application.OnTime Now + TimeValue("00:15:00"), "saveIt"

End Sub

Thanks for your help.