Performance issues with Serial communications

[BRDrew]

I'm using Pi4J on a project that is using serial communications to interface Raspberry Pi with Arduino Nano.
Basic serial communications is working, but I am suffering a 52ms delay from the Raspberry Pi receiving the response back from the Arduino and the Pi4J serial library passing it on to my Java program.
I've hooked up a scope on the communications link and can see the serial data transferring from the Pi to the Arduino and the immediate response going back.
Can any one point me to where I should look to try and determine why the Java Pi software is taking so long to receive the data coming back?
Using Pi4J 1.4 on a 4B, with UART0 ("/dev/ttyAMA0") running at 115200 baud.
While waiting for data to be available on the receiving thread I am using Thread.onSpinWait() to release the processor.
Any assistance would be much appreciated.