This will work.
main() {
double n1 = 15.00;
double n2 = 15.50;
print(_formatDecimal(n1));
print(_formatDecimal(n2));
}
_formatDecimal(double value) {
if (value % 1 == 0) return value.toStringAsFixed(0).toString();
return value.toString();
}
Output:
15
15.5