Does the cat have to be that close to the exhaust heads? I know it needs to be hot for it to work but can I get a way with it being 1.5m away from the manifold?

my understanding of the science is that the cat is placed close to the engine so that it get hot as quick as posible so that the time it is not doing its job is made as short as possible .on my N16 there are two cats on in the end of the manifold and one about 1 m away .keep it as close as posible but in the end check with your licenceing authority to see what they require.
best wishes
Iain

The main criteria for the "CAT" to work efficiently is temperature,so it must be fitted as near to the manifolds as possible, before any silencing.
"CAT" light up temperature is about 250 degrees centigrade, with optimum temperature being between 400 to 500 degrees, so its still going to work at 1.5m its just goig to take a little longer to reach "light up" temperature, and would operate at the lower end of its optimum temperature ,depending on engine fitment,and how long your manifolds are.
My fireblades cat is 1.3m away from the top of the manifold,when it was checked before SVA, the cat started to work after only 2 to 3 minutes.

Yes if it's too far away then it may never get to operating temperature for emissions test as these are obviously not done under load conditions. They do rev the engine to 2500-3000 RPM for a time before taking an emissions sample but that might not be enough to get it working correctly.

Good luck,
Craig.

Yeah, I'd basically echo what has been said above, as close as practical. If running fuel injection its also good to go with a heated O2 sensor, as thats the other half of cold starting emissions. Cheers!