The download isn't even remotely that big. If you are talking about the compiled size, you only need to build what you use (look up the --with-<library> and --without-<library> switchs).

You can also use the included bcp utility [1] to extract a subset of boost.

[1] http://www.boost.org/doc/libs/1_64_0/tools/bcp/doc/html/inde...