Araik

var a = 70;
var b = 15;
var result= [];

num = (a - (a % b)) / b;

for (i=0; i < num; i++) {
  result.push(b);
}

if ((a % b) < b && (a % b) != 0) {
  result.push((a % b));
}

console.log(result);  // (5) [15, 15, 15, 15, 10]

var a = 70;
var min = 5;
var max = 15;
var result = [];

function getRandomIntInclusive(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min + 1)) + min; 
}

while (a > 0) {
  b = getRandomIntInclusive(min, max);
  a = a - b;

  if (a >= 0 ) {
    result.push(b);
  } 

  if (a < 0) {
    b = b + a;

    if (b < min) {
      _t = min - b;
      b = b + _t;

      result.forEach(function(item, i) {
          if ((item - _t) > min) {
            result[i] = item - _t;          
            _t = 0; 
          }
        });
    }              
    result.push(b);
  }
}

var result_sum = result.reduce(function(sum, current) {
  return sum + current;
}, 0);


console.log('Сумма всех чисел: '+result_sum); // 70
console.log(result); // (7) [15, 6, 10, 7, 5, 15, 12]