2,77 MB is not small for a regular file. Maybe there are unused definitions inside? Would try file/cleane up document.
It's not that large though either. My guess is every blurred objects have a separate blur filter definition.
If the objects don't overlap, instead of blurring them one by one, grouping them together and blurring the group would be more "space-efficient".
60s is a good responding time. If you export the screen at a 96 dpi resolution, theoretically that would take the same amount of time zooming in for 100% zoom level.
In that manner, if you export at double resolution, it would take as much time as rendering the image on screen at 200%. Probably at some zoom level the area you want to export is larger than the one rendered on screen, but as a basic compare you can test with the zoom level rendering the blurring takes exponentially larger amounts of time.
Can show you svg-s that take 30 mins at least to export as the result of extensive use of filtering. And there are others which just melt the renderer right away.
The second issue, rendering to an external drive, I'm not sure of. My guess is the writing speed of the pendrive is smaller than what inkscape can perform upon exporting and the computer cannot handle/refuses to handle cached datastream of the saving process.
Doubt if a different inkscape version would give a boost to the performance. Only difference I know of is linux systems have inkscape work a bit faster.
For performance testing, made a collection of all sorts of svg-s
here.