List most recent items combined from Channel and Structure sections If we pass through an array of Channels &amp; Structure sections we find that Channels entries tend to be listed first. So the first 15 will comprise of ChannelOne and ChannelTwo and then start listing the Structure section. 

{% set homepageEntries = craft.entries({
    section: ['channelOne','StructureOne',channelTwo','StructureTwo'],
    limit: 15
}) %}

{% for item in homepageEntries %}
{{ item.title }}
{% endfor %}


All we want is a list of the 15 most recent items from a number of sections.

It does not look to be as straightforward as it seems. Creating multiple arrays of ids and merging still seems to produce the same results.
I was presuming that the default Order for Channels and Structure was postDate desc. But it turns out the default for Structure is sortOrder

{% set homepageEntries = craft.entries({
    section: ['channelOne','StructureOne',channelTwo','StructureTwo'],
    order: 'postDate desc',
    limit: 15
}) %}


Explicitly stating the order seems to fix this issue