List-class variable slower than ArrayList-class variable

Question

when I create List - program executed for 2.5 ms, if I changed List to ArrayList - program executed for 1.1ms.... who knows why?

class StockSpanner {

    ArrayList<Integer> list; //1.1 ms
    //List<Integer> list; 2.5 ms

    public StockSpanner(){
       list = new ArrayList<>();
    }

    public int next(int price) {
        int less = 0;
        int counter = 0;        

        list.add(price);
        counter = list.size() - 1;

        while(counter >= 0){
            if(list.get(counter) <= price) {
                less++;
                counter--;
            } else {break;}
        }
        return less;
    }
}