The three TV categories 1500, 800 and 500 (kbps) would seem to relate to the different resolutions you can view SD content.
1500 kbps is the required bitrate for fullsize SD (832 x 468) (just shorter than the width of the website) - this is the default size when you navigate to the TV show (assuming your connection can cope). This is also considered "Normal ...
To watch iPlayer on a Mac without Flash make it appear that the computer is an iPad.
To do this with Safari web browser turn on the "Develop" menu.
Then select "User Agent>iPad".
The only disadvantage is that the picture is iPad, or smaller, size.