There are plenty of opportunities for component build optimizations. Consider re-using previously built RPMs by simply tagging the old RPMs into the new tag without rebuilding them. This should only happen if all of the following conditions are true:

1. The buildroot as defined by the modulemd specification hasn't changed at all; i.e. the module-level build dependencies haven't changed -- no new deps, no deps removed, no stream changes and exactly the same versions are used.
2. The buildorder affecting your component hasn't changed, everything that was built before it in the previous version must be built first now as well. Any included modules need to be checked, too. Recursively.
3. The git hashes of both your component and everything that is scheduled for build before it (see above) haven't changed.

Also consider re-using RPMs built as part of other modules but that might add another level of complexity...