CHUWI AeroBook Plus 15.6 - wifi so slow

I have purchased CHUWI AeroBook Plus 15.6 inch Intel i5-6287U but compared to my old DELL is very very slow with internet working in WIFI. Is it a common problem or should i suppose that the wifi card inside the laptop is damaged?

I have the same problem last days.

I think that Intel wifi card caused the problem. When I pług on external wifi card to USB port, wifi works properly.