I do not think it is over optimized, if the results in € 200,000 candles are good I think it is a period long enough to prove that it is a robust strategy. Different would be a 3 month or a year backtest, 200,000 candles are more than 2 and a half years old. The strategy in the coming months will earn a little more or a little less, but the numbers must be similar.
If the strategy was originally optimised on 100k candles and then works equally well on 200k candles then that is a good sign. However two and a half years of back test data is an absolutely tiny amount of data to put any trust in at all let alone risk real money on in my humble opinion.
