With incremental builds. I have forked this project: https://github.com/wekan/wekan (~ medium size). On a 2014 macbook pro, reloading after a change in a template takes 10s. Not a dealbreaker, but this is frustrating. And this is with meteor 1.2. The slow build times may be due to the wierd frontend preprocessors (jade and stylus), but still.
Wekan author here. On my computer hot reload takes roughly 5s [Thinkpad T440s, ubuntu, 12go of RAM]. I'm not sure if the jade and stylus compilers add some time in the case I only modify JavaScript files, but anyway I plan to migrate these two package to support the new compiler API.
Still 5s is far from ideal considering the development experience with webpack and React hot loader.
This was my worst case and I did get it down to around 5-6 seconds by removing some Meteor packages (Meteor Toys in particular added a lot to build times but I also removed Velocity testing).
I believe they were incremental builds. Whatever happens by default when you make a change to a file.