Q: Slow download of OS X Installer for El Capitan

I'm having the same issue. I started the download on Sunday. My MacBook kept going to sleep so I set it to never go to sleep. It's been two days now and it's only half way through but it looks like it might be stuck now.

First, make sure your Mac can run El Capitan >  Upgrade to OS X El Capitan - Apple Support

El Capitan requires at least 9GG's of storage space. You can check available storage space by clicking your Apple  menu > About This Mac > Storage.

If your Mac meets the requirements and there's sufficient disk space, restart your internet modem and Wi-Fi router if you use one then restart your Mac and try downloading El Capitan again.

I updated my DNS per this post and it worked like a charm!!! Other posts about updated DNS didn't work. OS X El Capitan download TOO SLOW