What are you comparing it to? Have you run any of the ME7-based ROMs out there? The newer camera firmware takes away some of the shutter lag. Though I wouldn't say it's 100% perfect, it's much better than MDK-based ROMs.
Regarding AOSP, I've run PAC RC1 (4.2.2), and the stock camera on that is pretty quick. But I wouldn't say it's quicker than ME7 ROMs, and the TW camera demolishes AOSP feature and interface-wise.
I have yet to try focal or any 4.3 ROMs, though, so maybe the camera has improved. I did run the 4.3 Photosphere camera/gallery APK awhile back on TW, and found it to be about the same as the PAC-stock camera in terms of speed. I mostly used it for Photosphere anyway.