I'd set the rainmeter update to be refreshed once per second (Update=1000 under the rainmeter section of your skin), I would add a measure "Counter" with a maximum value of 900 (=15*60), and a "IfEqualValue=900" ,"IfEqualAction=PLAY [soundfile]"
Sorry it took so long to reply. I completely forgot about this query. Thanks Yali. I'll try that as soon as I get a bit of time to "play". I'm sure I wouldn't have figured out this structure on my own.
Yoc, Sorry it took so long to get back (health issues).
The short answer; this works!
For some reason I can't keep a clock accurate on my system unless I set Update way down. In my case to 50.
To play a sound, all you need to do is place a wav file in the specific folder and in the ini put: IfEqualAction=PLAY [*****.WAV] wherever you've shown it in your example. The soundfile name needs to be exact, with its extension and I think it is case sensitive. I like that you've set it up so that a different soundfile can be used every 15 min.
Temporarily, I put this in a little graphics skin I already had on my desktop so I can exit it and kill the sound should I need to without effecting my clock display. Gonna make a classier solution for this when I can find more time to play.
Update2. I originally was using a separate soundfile for the hr. seems you can only use 1 sound per ini. So, now it works but it looks like I'll have to make separate inis for each sound unless someone knows how to trigger more than 1 sound at different times in one ini.