Website will not start in Visual Studio 2015 Enterprise, but works fine in 2013 Pro

I'm having a problem running a website from VS 2015 Enterprise, where I don't have an issue running it from VS 2013 Pro. The error I get is:

This configuration section cannot be used at this path.
This happens when the section is locked at a parent level. Locking is either by default
(overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny"
or the legacy allowOverride="false". 

Error Code: 0x80070021

Config Source:

<authentication>
<windowsAuthentication enabled="true" /> <-- this line is red
</authentication>

I have also set the machine.config values to Allow for all tags, as well as the applicationhost.

Also, when trying to run it directly from the IIS Server Manager (pointing to the same location as the source files), I get a 503 Service Unavailable.

I can provide more information if needed.

Other solutions I have tried:

• https://serverfault.com/a/221501
• https://serverfault.com/a/516921
• https://serverfault.com/a/560492
• https://stackoverflow.com/a/12867753
• https://stackoverflow.com/a/12343141
• https://stackoverflow.com/a/10390085

I was able to solve this by modifying the applicationhost.config file, within the .vs folder of my solution, and marking the specified elements to allow override.