interval timer

Am looking for suggestions. Need a iOS timer app for someone who is visually impaired and quadriplegic. Person needs a subtle reminder every 15 minutes, throughout the entire day. Person uses voice over as their access. Looking for something they can turn on at the beginning of the day and turn off at the end of the day, independently. Also looking for something that just has a short beep at the 15 minute interval, then resets automatically, throughout the day. Have looked at the following types of apps: fitness timers, interval timers, pill reminders, stand up reminders, drink water reminders. Haven't come across one that is doable yet. Any suggestions appreciated, even non-application suggestions.