You can switch to "Notify" event handling to make it faster.
If you use EventResizeHandling = CallBack the sequence is as follows:
1. The user finishes resizing.
2. The calendar/scheduler sends a request to the server-side event handler using an AJAX callback.
3. You make the DB changes and reload the events.
4. The events are refreshed on the client side.
Basically it waits until the roundtrip is complete.
If you switch to "Notify" mode it will look like this:
1. The user finishes resizing.
2. The calendar/scheduler is updated on the client side immediately.
3. The server-side event handler is called.
4. You save the changes to the DB but you don't have to reload the events.
See also:
http://doc.daypilot.org/scheduler/event-resizing/
The same applies to event moving:
http://doc.daypilot.org/scheduler/event-moving/
Let me know if it didn't help.