The user role has all the permissions to Design Studio, but whenever trying to preview an email, a limited access message is displayed:
"You do not have sufficient privileges to perform this action"
The user role must have permission to 'Access Database'. The full access to Database is not needed, just the main access by selecting 'Access Database' and unchecking everything else underneath
The reason for this permission is the fact that when previewing emails, you can select to preview an email as a specific lead. In order for this to happen, users will need access to leads.