i put an A15 into my 1200 wagon on the weekend and used the carby off the A12 as i just rebuilt it, and it looks exactly the same as the A15 one.
Problem is, the car drives fine while it warming up and i have the choke on, but once i turn the choke off it hesitates during any sort of acceleration, so ive been drving it all week with the choke slightly on so it drives normal.

So im just wondering whether the jets are bigger in the A15 carby or if there is some other difference between them, or whether i should start looking elsewhere for the problem?

any ideas would be great as this car is my daily driver

yes i think the jets in a a14 carb are bigger but i ran a 1200 carb on an a14 for a long time with absalutly no hassle i would be checking for vacume leaks how did you recond the carb did you blow it out with carb cleaner and an air compressor? did you replace the acceleration plunger? is the float set properly?

In usa models, A12 jetting is richer than A15 jetting (it is a combination of the jets and the air bleeds). We had a discussion about this a month or two ago.

If you rebuilt the carb, it is possible something is wrong with the re-assemble -- I do that all the time, carbs are tricky.

I had a similar problem when I rebuilt my carb. I realised that I forgot to insert the little ball bearing into the Acceleration pump cylider. And also Spray some compressed air into the jets just to make sure. :)

When i rebuilt the carby i replaced all the parts that came with the kit and blew compressed air thru it all and cleaned it with carby cleaner.
I was also extra careful to put everything back where it came from.

After i rebuilt it i had it running on the a12 and there were no problems with it at all.
Guess ill have to pull it all apart again and swap all the internals over

If the carb ran fine on an A12 engine before you fitted it to the A15, wouldn't that suggest that there is nothing wrong with the carb itself? Perhaps it's the 'instalation' that's the problem.
Is the gasket under the carb undamaged? Are all the vacuum hoses correctly connected & in serviceable condition?
As a confirmation check, does the carb squirt fuel when you quickly open the throttle?
Is the inlet manifold sucking air at any other point, like Vacuum brake plumbing [if fitted] or at the port face.
How is your PCV valve, is it doing what it's supposed to do?

Grab your workshop manual & check these things as per the troubleshooting section.
Rebuilding the carb if it isn't the cause of the problem can be a frustrating exercise so try to do your diagnostics first.

The worst a stock 1200 carb should do is to provide a lower level of overall performance, not give the symptoms that you describe

EDIT
The accelerator pump arm has a couple of positions to place the link rod so as to give a greater, or lesser, squirt of fuel. Try the inner position for a greater shot of fuel during acceleration.