Parallel testing runs at different speeds depends on version phone

I have developed a code in order to run parallel tests in different devices(2 Nexus Huwei 2015 and one Samansung LG) using testNG and appium(by setting bootstrap port and UDID of every device).And when I am executing the test, It runs faster and in parallel both Nexus phones, but there is an execution delay of 6 seconds running test in the Samansung LG.

Do you know why is happening?, Do I need to do something else?, I want to execute the test in parallel on those 3 phones.