title: Composer satis, time to build private packages
body: <p>I have many private repositories at Bitbucket, there are about 100 repo's (+/-). Time to build them by <code>php bin/satis build</code> takes a long time, somewhere about 3 minutes. How can i refresh one repository or optimize time of building. Because i saw some satis configuration, where <code>config.json</code> file contain more than 4000 repositories. I can not imagine how many time need to build all of this.</p>