Happy New Year 2016. May God bless us with health and prosper.
Okay, just quick update. I found quite annoying fact: VirtualBox version 5.0.4 has bug: in bridged adapter mode, host can not ping guest VM and vice versa!
I googled about this and some people had early conclusion that it might be related to bugs in NDIS6 adapter.
However, there is easier workaround: just make sure you upgrade to latest version (version 5.0.12 as January 12th, 2016). Or, just stay in 4.3.x version. In my personal opinion, so far version 4.3.x ( which is still in active maintenance mode) is more stable than 5.0.x.
Hope it helps somebody out there.....