A lot of that, though, is actually loading LaTeX packages itself.
TeX underneath is really very speedy; on my several year old laptop it can compile several hundred pages in around half a second (and pdftex takes around twice as long).
I believe it's also possible to perform optimal line breaking algorithms incrementally, so you wouldn't have to reset the whole document as you add to the end of it (although you may as you add to the start of it, but that happens in Word anyway).
TeX underneath is really very speedy; on my several year old laptop it can compile several hundred pages in around half a second (and pdftex takes around twice as long).
I believe it's also possible to perform optimal line breaking algorithms incrementally, so you wouldn't have to reset the whole document as you add to the end of it (although you may as you add to the start of it, but that happens in Word anyway).