Does Campaign Queue for Batch Campaigns Affect Email Processing & Delay Sending/Delivery?

@guitarrista82, batch and trigger campaigns are processed in separate queues (the article you have linked also states the same). Additionally, the campaign priority override feature that you mentioned is applicable to the trigger campaign only. You cannot override the batch campaign's priority. When several batch campaigns are in a queue, the normal campaign priority is based on the flow steps in each campaign, followed by Marketo (unlike trigger campaigns, in which you can override the priority).

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A couple of questions:

1. The table above says "Send email (triggered)" is considered High Priority - by "triggered" does this mean only emails that are sent via Trigger campaign are considered High Priority or do emails sent via Batch campaign get High Priority?

Yes- trigger campaigns with a Send Email flow step take the highest priority in the trigger queue. So, if you have more than one trigger campaign in the queue, the one with the Send Email flow step in it would be processed before the one w/o). I would think batch campaigns would also follow a similar priority order, but since the scheduling of batch campaigns is managed by users, I'd recommend you be a little cognizant and not schedule large batch campaigns at the same time/very near to each other such that it'd overwhelm the instance and cause campaign execution delays.

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1. The article says "High priority campaigns run first in the order they were added to the queue. Once those are finished, the next highest priority campaigns are executed in time order and so on down until all have completed." Question 1: When it says "in the order they were added to the queue", what is it referring to, when the campaign itself was scheduled or the time that the campaign is scheduled to send the email? So if I have two campaigns both scheduled to send an email at 7 am, which one will take precedence? Question 2: By "finished" does the article mean that the campaign has to completely process everyone first before the next campaign in the queue can begin processing?

This is referring to the trigger campaign queue IMO- when multiple trigger campaigns are fired simultaneously, Marketo processes them as per the priority order (default/overridden). If you have multiple batch campaigns scheduled at the same time, I'd think (and supported with some testing), that both the campaigns would run at the same time (i.e., at the scheduled time), however, if there are too many people in each (and additional things that'd put a strain on the instance - complex smart list, number of flow steps, choice steps and their complexity), you might see apparent delays in the campaign processing. By finished, the article means that once all the higher priority trigger campaigns in the queue are done processing (i.e., all flow steps in all high priority campaigns are done executing for all the qualified people), Marketo takes up the next-in-line priority campaigns (i.e., the ones with the Medium priority and then the ones with the low priority).

As a solution to your problem, you should use the Email Send program with the Headstart feature turned on. It gives you that option by processing the program in advance. With Head Start selected, the program will begin processing approximately 12 hours prior to the scheduled time. Once processing starts, the program is locked. Since people are processed 12 hours prior to the scheduled time, this is more likely to deliver emails to people on time than regular batch campaigns that process people in the smart list right at the time of the scheduled send. As said earlier, you should work on scheduling campaigns such that at least the ones with a lot of people in them don't clash/are scheduled right next to each other so you have minimal send and execution delays. Maintaining a campaign calendar is effective- Marketo also has one available OOTB.