The MPU6050's DMP fifo_data change very slowly

I have a question about MPU-6050's fifo sample rate using DMP's library.
but I found a issue was Datas which are Gyro,Accel and 3-axis quaternion changed slowly throungh function dmp_read_fifo(...) . why?
I use a host processor is BLE CC2541 of TI.

Thank you for your consideration of my problem.