If single device is use and you are operating in Byte ( x8) mode then you can leave the pins DQ14 -8 open/floating .
During BYTE mode access, the DQ15 pin is assigned as A-1, the least significant bit (LSB) of the address bus. Therefore, connect A-1 pin to the lowest address A0 of the CPU. DQ14-8 will be tri-stated (high-Z) and can be left OPEN/floating. The BYTE# pin should be set "0" (LOW).
In the app note it was mentioned that both the devices are in word mode x16 and since the example described it as 24 bit data bus the upper bits are connected to ground.