You can take a good look at all the internal here.
Points to be considered :
1. Its not Qualcomm.
2. Each and every part except for the IPS panel, 3GB RAM and 16GB internal memory is manufactured by Sony. (Correct me if I'm wrong)
3. It cannot be the internal storage as Galaxy S5 ships with the same.
So it has to be either the 3GB RAM from Samsung, probably that's why they didn't include it in their own flagship. Or the IPS panel. To me, it seems more of the RAM issue. What about you guys?