how to reduce transmission time

I am using XBEE-PRO-S2B module. The transmit frame is of 60 bytes. Each frame is taking on an average 400msec to reach the coordinator. As per some calculations mentioned below transmission time should be almost 2msec per frame of 60 bytes.
standard data rate of zigbee protocol = 25 Kbps
my frame length = 60 bytes
with reference to the standard data rate, data rate of frame created by me comes as = 0.0192 sec

Due to this data rate issue I am facing the problem of data loss.
Kindly suggest me is there any settings which can be changed to achieve this data rate.

You are not taking into account the Rout Discovery function or the radios overhead for processing the data.

If you do not need the router function to repeat the message to extend the range, switch to the 802.15.4 product. It has less over head and a higher throughput.