Improve calendar loading speed - calendars gets much slower with more events

Currently customers are getting around this by truncating old events. Example:

The current way to backup Team Calendar is through exporting them to iCal. However upon restoring the iCal file format, all the events that are created after the export will be missing as it will load whatever in iCal file which is created before the events were created, and you need to create new Calendar.

It would be good if there is other option to backup Team Calendar that recognized the previous calendar, therefore it will replace the calendar and will have an option to choose either to keep the events that are created after the backup.