If 15V is applied to the 5V pin of XIAO, it far exceeds the allowable input voltage of 6V of the internal LDO (XC6206), so XIAO may be malfunctioning.
If 15V is applied to the 5V pin of XIAO, it far exceeds the allowable input voltage of 6V of the internal LDO (XC6206), so XIAO may be malfunctioning.