Dear Franco,
I think this issue depends on the system and the bandwidth from where you are running.
PMI ensures that all exam centres are adequately equipped to provide a good and reliable connection.
I did not noticed such slowness when passing my exam. Please do not add this as one of your concerns before the exam.
Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®