Try setting a "timer" for 15 minutes instead of an "alarm".
Not sure if this is a regional dialect thing, but in North America, a timer has a duration, but an alarm is set for a specific time, which would possibly explain the confusion.
While I agree it'd let the user use the system, the system should do the right thing for either situation, or at least abort and say it doesn't understand. That's the problem with LLMs so far. They can't admit they don't understand.