Aexploder is slow, indeed. But I achieve 3 minutes on mine A500 + HD when writing an ADF file into a disk. It is a rev6 PAL/NTSC (1Mb Agnus) using 2.04 ROM (37.299).
The candidate of a culprit in this case is your cable! 2+ meter of cable without shielding is a major no-no for serial transfers.
Also try lower transfer rates to less than 19200 (14400 just for testing purposes and use baud bandit device instead original serial.device .
