Q: 2 days and 5 hours to download El Capitan?!

that number will re-adjust itself as it goes

but in the mean time if you can use a cable over wi-fi it will be faster

and if you can suspend any other device on your network that is using the router it will also be faster.

if it's not moving you can take your mac to an Apple Store and use their connection.

BTW t's a good practice to make a backup before proceeding in the event you break operability with a 3rd party application, utility or device.

Use Time Machine to back up or restore your Mac - Apple Support

Pause the download. Restart your Mac and router, then try again. You'll likely get a better connection to Apple servers. It should not take this long.

I had  Yosemite   I get up next morning i see   El Capitan  ??? No Idea how it happened  may be the hacker like it more???

So stay with the Yo,,,,