Xbee Zigbee througput very low

When sending data from one router to the coordinator, I get very low throughput, in my C code on the microcontroller i send datapackets of 7 byte at a frequency of 62.5 Hz via uart to the zigbee, the baud rate is 4800 (was originally higher, but I tried lowering it to solve the problem, didn’t work). The data gets to the coordinator (connected to my laptop) but at a low throughput with high latency, when looking at the CTS of the router I see that it periodically goes high. This is not even close to the throughput which should be achieved, any idea how this is possible?