how to send a file of 6 KB over xbee s2 series?

I am trying to send a file of size 6 KB over the xbee module using raspberry pi. If i send the file all at once, it takes me about 3 seconds to receive the file. How should i efficiently send the file over less than a minute because i guess 35 KB can be sent per second(250 kbps).

I would guess that you are broadcasting to all radios. When broadcasting packets on the series 2 you are limited to about one packet per second. Check that you have a destination set (DH, DL) to improve your speed.