Are you committing the composer.lock file in your projects? Likewise you should try and use as close to absolute version numbers as possible in your composer.json `requires` sections.<p>I used did a quick test (having run `composer clearcache` each time) on one of my projects:<p>Without composer.lock: 
Memory usage: 75.96MB (peak: 87.5MB), time: 38.54s<p>With composer.lock:
Memory usage: 7.47MB (peak: 8.99MB), time: 28.6s