Every now and then we get asked why we have a limit of only one post per 15 minutes per Instagram account (i.e. not your Schedugram account).
This is for a very important reason for us -- it's to "spread the load" of the images over a period of time.
Firstly, if you posted three images at 9am on one account there could be issues with how they are ordered in a particular sequence (which matters to some users). Same issue if there is problems or congestion with the service, as things might "run together" during a delay.
Secondly and more importantly it's to prevent abuse of our service. Because we don't just have API calls that upload the photos (a tablet has to actually be tasked with sending the images), there is a significant risk that abuse would occur if we didn't have at least some kind of rate limiter.
While this is frustrating for some brands, particularly those looking to put out a series of images around a particular key event, it's not something that we can really budge on. Prior to having this limit in place, the whole Schedugram platform would regularly go down as a result of one user flooding a particular timeslot with 100 images (one every minute for the same account)...usually spammers of course.
We are careful to avoid facilitating any such use of Instagram for two reasons: firstly, it's against Instagram's community guidelines and terms, and secondly we don't think that it's good practice or fits with the "ethos" of Instagram -- brands shouldn't be annoying as hell to their followers. Even one post every 15 minutes could be incredibly frustrating to users if done all day, every day!
Furthermore, spreading out images over time means that we can offer a better service to all of our users, particularly those who post the "standard" 2-3 images spread throughout the day. If their images were being delayed by someone flooding the service I'm sure that they would be quite disappointed.
If you are looking for a solution that would allow you to post more frequently, we're happy to discuss your use case with you and set you up with an enterprise plan if you would like. We do this because then we can make sure it's not going to be inappropriate use of our service or Instagram itself. Enterprise customers have dedicated hardware (i.e. their own tablet(s)), so they can post as many images they want at the times they want -- their posts are just limited by the number of tablets attached to their account as things would be queued in sequence for that account. This also means they will only delay their own posts, which we think is appropriate.