How can I repeat the Speak Cell in intervals, once in two minutes?

Assuming you want Excel to convert a cell content to speech every 2 minutes, you can do that based on Don's tutorial here Run a Macro at Set Intervals in Excel

In the attached file, I've just modified Don's code from that to:

   1) rename his macro "mymacro" to "Speak_At_Intervals"

   2) replace the run command in that macro from MsgBox (now commented out) to  

Application.Speech.Speak Cells(3, 3).Text & Cells(3, 4).Text

- this  makes Excel say an introductory phrase in cell C3 plus a number in cell D4 (the kind of value I assume your spreadsheet is recaculating)

   3) set the "interval" in Sub macro_timer to do that every 2 minutes.

You can run  "Speak_At_Intervals" alone, just to see how that works, but to get it to speak every two minutes, run "macro timer"

REVISION (reflected in revised file "Speak cell contents at intervals v0_b.xlsm" attached) : If you have a monetary number to be spoken, Excel will do that if the cell is formatted as currency (but the value will remain a number e.g. 3.27)

Note that you can use Sub stop_macro to stop the repeated speech.

Full code is here:

Public interval As Double
Sub macro_timer()

interval = Now + TimeValue("00:02:00")

'Tells Excel when to next run the macro.
Application.OnTime interval, "Speak_At_Intervals"

End Sub
Sub Speak_At_Intervals()

'Macro code that you want to run.

'MsgBox "This is my sample macro output."
Application.Speech.Speak Cells(3, 3).Text & Cells(3, 4).Text

'Calls the timer macro so it can be run again at the next interval.
Call macro_timer

End Sub
Sub stop_macro()

Application.OnTime Earliesttime:=interval, Procedure:="Speak_At_Intervals", Schedule:=False

End Sub

Not sure if this will work within your updating data file but good luck.