I have a 2015 iMac. I erased the Macintosh HD in disk utility. Is there a way to fix this?

Hey there!

Try to follow these steps:

1. Start up from macOS Recovery: Turn on your Mac, then immediately press and hold these three keys until you see an Apple logo or other image: Command (⌘), Option, and R. 
2. Select a Wi-Fi network from the Wi-Fi menu (top right).
3. From the utilities window, select Disk Utility and click Continue.
4. Select View > Show All Devices in Disk Utility, and select the top-level "APPLE HDD" entry.
5. Click the Erase button in the toolbar, then enter the requested details:
   1. Name: Macintosh HD
   2. Format: APFS or Mac OS Extended (Journaled), as recommended by Disk Utility
   3. Scheme: GUID Partition Map
6. Click Erase.
7. When done, quit Disk Utility to return to the utilities window.
8. Select Reinstall macOS in the utilities window, then click Continue and follow the onscreen instructions.

Let us know if this works!

-Jack

Boot macOS Recovery: How to reinstall macOS - Apple Support

On that screen, select Reinstall macOS.

You need to head to Disk Utility in Internet Recovery mode by using the Option-Command-R at boot.

-Jack

It sounds like you formatted the start up drive which erases EVERYTHING! Assuming you use Time Machine ago back up this is just an inconvenience. If you did not back up well you are about to learn why backing up daily is critical. Please call AppleCare and they will walk you through the process. If you are in the USA that phone number is (800) 275-2273.

Good luck!

The HD may have failed? You cannot see the HD at all in ** when you boot into the recovery partition? Technically you cannot boot into the Recovery Partition if your HD is completely dead, otherwise you may be doing something incorrect.

Could you upload a photo of what you see?

To upload a photo, you can use the Image insertion tool.

-Jack

... and is Disk Utility not one of the four choices?

You have to get to that point.