At busy trading times of the day, backtesting sometimes runs much slower. A one-week backtest that might take just three minutes to run on a Saturday, for example, can take 15-30 minutes on Wednesday afternoon GMT. I have tried clearing the cache, unsubscribing from instruments, and rebooting the PC...no difference. Oddly, sometimes it takes a long time before the processing of ticks begins, but once the numbers start to click through on the screen, the processing speeds up.

Is this because the main Dukas trading servers are busy? Why would that even matter if the historical data has been downloaded. All backtest processing should occur on one's local PC.