I’m unable to reproduce this on my current development configuration (Quadro P6000, Win10-64 1607, 397.64 drivers) with the precompiled SDK examples.
Either the OptiX 3.9.1 path_tracer.exe, the OptiX 5.0.0 optixPathTracer.exe, or the current OptiX 5.1.0 optixPathTracer.exe starts in under 2 seconds.
Have you by chance enabled OptiX exceptions inside the slower application?
At OptiX 4 the internal kernel compiler was completely rewritten to use LLVM and that will take a lot longer when generating the code for the exception handling than in previous versions.
That said, when switching to an OptiX 5 version, please note that OptiX 5.1.0 has just been released last week and that also contains changes to improve startup times in general.
Also the optixPathTracer inside the SDK is a very limited example. For some more elaborate path tracer implementation have a look at the sticky post in this sub-forum explaining the new additions to the OptiX Advanced Samples on github.