The update delay for the radar information is an arena setting (viewable from the arena settings like everything else). I'm guessing it is also a product of your connection and how fast your client can process the data coming from the host - the busier the arena, the more data is sent and the more data your computer needs to recieve and process before your screen is updated.
I don't think that's quite exactly right. The behavior I've seen and a vague recollection of something Hitech might've said seems to indicate the program updates the location for x number of aircraft at a time. So for example using random numbers to illustrate, if it updates 10 aircraft every 10 seconds, and you're in an arena with 10 aircraft in it, every 10 seconds you will see the update for a specific aircraft.
If you've got the same scenario and there are 100 aircraft in the arena, it will be 100 seconds in between updates for each aircraft, because it will have to cycle through the other 9 groups of 10 before it gets back to him.
It should have virtually nothing to do with your connection speed and everything to do with how many aircraft are in the arena.
Wiley.