Преобразование 5 минуток в 15 минутки

            readonly TimeSpan _timeFrame = TimeSpan.FromMinutes(5);

            string[] lines = File.ReadAllLines(@"C:\Users\user\Desktop\Торговля\Data\ROSN.csv");
            List<Candle> candles = new List<Candle>();
            foreach (string line in lines)
            {
                var parts = line.Split(',');
                var time = (parts[0] + parts[1]).ToDateTime("yyyy/MM/ddHH:mm");

                if (time < DateTime.Today)
                {
                    candles.Add(new TimeFrameCandle
                    {
                        OpenPrice = decimal.Parse(parts[2], CultureInfo.InvariantCulture),
                        HighPrice = decimal.Parse(parts[3], CultureInfo.InvariantCulture),
                        LowPrice = decimal.Parse(parts[4], CultureInfo.InvariantCulture),
                        ClosePrice = decimal.Parse(parts[5], CultureInfo.InvariantCulture),
                        TimeFrame = _timeFrame,
                        OpenTime = time,
                        CloseTime = time + _timeFrame,
                        TotalVolume = decimal.Parse(parts[6], CultureInfo.InvariantCulture),
                        Security = _instr1,
                        State = CandleStates.Finished
                    });
                }
            }
            int count = candles.Count<Candle>();
            int firstElement = 100; // вывод количества свечей из истории

            _candleManager.Start(_series);

            for (int bar = count - firstElement; bar <= count - 1; bar++)
            {
                ProcessCandle(_series, candles.ElementAt(bar));
            }
...
        private void ProcessCandle(CandleSeries series, Candle candle)
        {
            //_chart.ProcessCandle(_candlesElem, candle);
            _chart.ProcessValues(candle.OpenTime, new Dictionary<IChartElement, object>
			{
				{ _candlesElem, candle },
				//{ _longMaElem, longValue },
				//{ _shortMaElem, shortValue },
			});
        }