The only way to speed things up is to reduce the PTFE lengths and bends in the PTFE tubes. Reduce friction and length of the PTFE tubes.
I think if the AMS was built differently, cut in two parts between no2 and no3 feeders then re-connected with feeder 1 & 2 facing feeders 3 & 4. Fit the AMS Internal Hub Unit directly below the 4 feeders and then place the entire assemble on a frame 200 mm above the printer and have the AMS Internal Hub Unit feed directly into the filament buffer then into the extruder via a shorter PTFE tubes, the speed of filament changes could drop to 20 seconds or less. This will still not resolve the the wasted filament purged to clean the nozzle. This will also shorten, remove many bends and loops in the PTFE tubes and reduce filament getting stuck in the bends inside the AMS and between the AMS and printer. This would only work effectively for one AMS, if more AMS units are required the units would have to be mounted above the printer on a shelf feeding to the multi filament buffer straight to the extruder. This would make the printer and AMS unit profile higher by 150 to 200 mm’s.