Events in shared calendar very slow to appear

Hi,

I recently shared a calendar with another user and have noticed that events are taking a very long time to appear on both devices, sometimes in excess of 12 hours, is this normal behaviour or is something not working quite right? I believe we are both on iOS 9 and all the other issues I have found on the net regarding this seem to be related to old OSs.

Any suggestions would be greatly appreciated.

Thanks