Have a look at the following post that explain some basics why your model may run slower.
Hailo Community - My model runs slower than expected
In your case you should check whether your PCIe is set to Gen 3.
Also when you compile a model there can be differences in speed between versions of the compiler and the compiler has a performance mode where it will try harder to achieve a higher throughput. This will increase the time needed to compile the model significantly. So, the same model can be compiled into HEF files that run at different speeds depending on the effort used to compile it.