1) If your shape-file of 5mb contains 245 polygons, then these polygons contain a lot of points. So, it is rendered very slow.
When you have a need to show a large GIS data on the map then I would recommend considering a possibility of server side rendering of GIS data to the tile images like it provides the OpenStreet and Bing.
2) Unfortunately it is hard to say about particular causes of this problem without your shape-file, but using the stack trace you sent. Most often this problem occurs when the DBF-file contains the asterics symbols in numeric fields. It can occur because of the arithmetic overflow when inserting a data to DBF-file.
3) The current version of the map control cannot help to resolve the performance issue for large GIS data anyway.
the Telerik team