[Onno Kreuzinger]

hi
it is 10 frames per sec., pal is 25 so 15 would not work (cinema movies are at 24, and one mpeg standart is defined at 23,89..)
also tv uses interlave, this "enables" the human filter in your brain, which puts those half frames together. thats why viewing tv makes you faster tiered (you eyes).

when you get tired it gets slower, close to 6 frames/sec, you can test it with avi's, before you go to bed you will be able to view movies at 18-20 frames/sec without noticing. this also lead to "how long is a moment", according to studies one moment is about 1,5 seconds when you are fit, and it goes up to 3-4 seconds when you get tired. but that is psychology... :-)