[Steeveedee]

15.5 is in the charging range, but a bit high. Maybe you should shut it off and look to see if something is still draining the battery, or if it is fully charged. A fully charged battery is 12.6V. Minimum charging voltage is 13.5V. Anything below that, you have a charging system problem. Charging at 15.5 seems to me like the system is picking up from a low charge state.