nrfjprog programming is slower for 52840 chips

[koniho]

We have noticed that using nrfjprog for programming 52840 based devices (and the devkit) that programming times are longer than with 52832 based devices with the same size hex. Is a difference expected?

[haakonsh]

Well if that includes the time it takes to erase the flash first then yes, because erasing flash is more time-consumption than writing to it and there's twice as much flash in the nRF52840. 

You can experiment with using sector erase as it only erases the flash pages needed by a given hex file. See nrfjprog commands --program's optional commands.