One technique I used is to download updates directly via

    wget -c --limit-rate=200K http://support.apple.com/downloads/DL1833/en_US/osxupd10.10.5.dmg

-c resumes download where left off, the rate limiting can be used to match the speed of your connection or intermediaries reducing stalls, drops and angry network users. I would often keep a list of URLs in `download-queue.txt` and use the above flags with -i to load the list of urls, letting it run overnight at some much lower speed.