Hey @pray4afghans,
Thanks for reporting this! We've confirmed the issue and have a fix underway.
When a campaign only allows 60 minute slots, the sign up tool was still saving each sign up as 15 minutes, which is why the confirmation email shows 15.
Each sign up still counts as covering its full hour on the campaign calendar and coverage percentage, but the total minutes only count 15 per sign up.
It will be in the next release. You can follow the fix here: https://github.com/DiscipleTools/disciple-tools-prayer-campaigns/pull/440
We'll post here once the release is out.