Download slow El Capitan maybe stuck

The download speed is showing as 39KB/s which is very slow. Sometimes downloads from Apple can be slow....even painfully slow at times. Sometimes starting over may get you a better connection with Apple's servers....sometimes not.

You can download that El Capitan installer using any computer since it is accessed from outside of the Apple App Store, but you will need to use that downloaded file on a Mac that is compatible with macOS 10.11 El Capitan which is generally models listed as 2007/8 to 2015. The .pkg executable file found within that DMG file will only run on those older systems, so you won't be able to create a bootable USB installer for El Capitan with any 2016+ Macs.

If you have an 2007 to Early/Mid 2009 iMac, then you can try using local Recovery Mode by booting with Command + Option + R as long as you haven't erased the drive yet and assuming the internal drive is still healthy (while you can use Command + R, the extra Option key should prevent needing to associate the installation with your AppleID). If you have a Late-2009+ iMac, then using that same key combination should result in accessing Internet Recovery Mode to access the online macOS installer.

a brody wrote:

If your iMac is not older than El Capitan, you can't use that download to get El Capitan.

FYI, any computer that can access the Internet can download this DMG file since it is being downloaded from outside of the App Store.

However, only those models you listed can actually run the .pkg executable found within that DMG file to extract the full installer & create a bootable macOS El Capitan USB installer.

I forgot to include the following link to the OP, but it is a good reference to identify the exact models which are compatible with various versions of macOS (I wish Apple did this for easier reference & identification):

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

If your iMac is not older than El Capitan, you can't use that download to get El Capitan. Any Mac older than

September 30, 2015 but newer than July 21, 2011 will support that installer.

Older Macs will also support the installer, provided that Lion is installed first. These older Macs with [Device ID/Machine ID] (explains how to find it). Finding a working copy of Snow Leopard 10.6.3 retail for Macs older than March 15, 2010, or the original 10.6 installer disc can be a challenge for those older Macs, and upgrade to 10.6.8 combo to get the App Store to be able to install Lion is also a challenge:

MacBook (Late 2008 Aluminum, or Early 2009 or newer) [5,1 or 5,2]

MacBook Pro (Mid/Late 2007 or newer) [3,1]

MacBook Air (Late 2008 or newer) [2,1]

Mac mini (Early 2009 or newer) [3,1]

iMac (Mid 2007 or newer) [7,1]

Mac Pro (Early 2008 or newer) [3,1]

Xserve (Early 2009) [3,1]

command-option-shift-R boot on wired keyboard will install El Capitan on Macs released the year of El Capitan's being the current OS starting September 30, 2015 and ending September 19, 2016. You will want to connect such a Mac to Ethernet or Thunderbolt 2 to Ethernet adapter if Ethernet port does not exist.

There are some scenarios where the installer can't be verified because of the computer's date and time:

https://appuals.com/this-copy-of-the-install-os-x-el-capitan-application-cant-be-verified/