This was an interesting one. 15 seconds, 143 frames, 256 colors, 25 fps, 2.7 MB. Not a whole lot changes from frame to frame so I figured I might be able to pull off such a long gif.
Photoshop has a dither % setting, with 100% generally looking the best. Lowering this setting increases banding and reduces the file size. Dropping dither from 100% down to 99% got massive savings this time. That's apparently something that works well when you have all these near identical frames.
And of course transparency's on. That saves a ton.