Most likely it’s not re-analyzing the track. If you are importing the track for the first time it’s generating the waveforms it needs to play the tracks back. So it’s not recalculating the beat grid but just doing some internal stuff.
It should only need to do this once when the track is first imported to the collection. Subsequent imports should ask ‘want to overwrite meta data’ and after saying yes, no analyzing should take place.
Please note that this step is necessary so disabling auto analysis in the rekordbox is not a good idea. rekordbox needs some of this info in order to display cue points and beat grid correctly so in some cases this may cause beat grids and cue points not to display correctly.