Instagram increasing video length to 60 seconds, allows iOS users to stitch together videos5
Instagram also made another announcement which might put a smile on the faces of iOS users who enjoy the app. Soon, they will be able to stitch together multiple videos into one. And with the new 60-second time limit on videos, this will give them an opportunity to show off their creative side. Again, this is limited to Instagram subscribers using iOS.
You can check to see if your phone has the new version of Instagram installed simply by taking a 60-second video and posting it. If you have no problem putting up a message with a one-minute video, congratulations. You now have the latest version of the app on your handset. If the update hasn't hit your phone yet and you're limited to posting 15-second videos, don't panic. The latest version of the app will hit your phone shortly.
source: Instagram via RedmondPie