Less dependencies rebuilds too frequently with less.js

We have a lot of less, it compiles to 300 + 400 kb css files.
Compilation takes 20-25 seconds.

I switched from lessphp to less.js (and fixed issue with relative urls) and profiled compilation.

I found that compilation actually takes only 8-10 seconds and then 10-15 seconds spends for build dependencies for watch source files changes.
Dependencies rebuilds at every less compilation, but files don't adds or removes frequently.

I think that rebuild dependencies only after cache clear will be enough. It speeds up less rebuild at 50-70%.