I am getting slow internet speed on Ubuntu 16.04.1 LTS in virtualbox on host windows 7. I am using ethernet cable but download speed is half of my internet plan. Please help me.
The only way to test this is to get Ubuntu out of the VM, and run it on real hardware. There are "live" versions of Linux (not just Ubuntu), bootable off DVD or USB, where you can test the "real" network speed using "real" hardware.
If Internet performance is so important for your project running on Ubuntu - get it on real hardware.
Running inside VM is not same as running on real hardware. The host computer must "transcode" the network traffic between its network adapter, and "software" adapter on the VM, so what you get is more or less relevant.
The only way to test this is to get Ubuntu out of the VM, and run it on real hardware. There are "live" versions of Linux (not just Ubuntu), bootable off DVD or USB, where you can test the "real" network speed using "real" hardware.
If Internet performance is so important for your project running on Ubuntu - get it on real hardware.