It appears amazon does not allow downloading any upgrades below current (15.6.5).
The website returns the following error:
```
This XML file does not appear to have any style information associated with it. The document tree is shown below.
<Error>
<Code>AccessDenied</Code>
<Message>Access Denied</Message>
<RequestId>E43HHJ0B7TF2TJCB</RequestId>
<HostId>Kp6eoI+6gIFmA9rXOeQzScp1O+oVN0LwfisL+rvnGB cWTmvaDjOMT2b8MDjhUYLzgtUrlUeEdB0=</HostId>
</Error>
```
I was able to find the update
here