can I get noise of 24G with accelerometer configured at +-16G
A value of 0x7fff on the output works out as 24 g so yes, in theory you can get that as an output value. However it also means that your sensor is well outside it's calibrated range and is possibly clipping so the value is fairly meaningless. About all you can say for sure it that it's something a reasonable amount over 16 g.

It could also potentially be a bus timing or read error causing you to get invalid data, I would expect that to give 0xffff or 0x0000 (0 or -0.7 mg) but 0x7fff may be possible in that situation. If the rest of the data is valid then that's unlikely to be the cause but if you don't think there is a chance the system got knocked then it's worth looking into.