That would be a 15 second setting (5 seconds per ring - voicemail works by time, not by rings).
In your voicemail voice menu, there's an "Advanced" or "more" option, and in there should be something about settings or about time to go to voicemail. Set that to 5 seconds per ring plus about 2 seconds. (The ringback your caller hears isn't synchronized with the ring you hear, so the 2 second slop allows you both to hear the same number of rings.)
The reason I can't be more specific is that different carriers use different voicemail server software at different times, so even if I knew what your carrier used 2 years ago, they may have it set differently now.
If you can't figure it out from listening to the prompts, call your carrier's customer support number (from a different phone) and they can walk you through it or set it for you (depending on the carrier).
08-10-2015 02:08 PM