no wifi in Ubuntu 15.04 [duplicate]

Your device is covered by default in Ubuntu 15.10 although it requires firmware that is not installed by default but can be added later. My first suggestion is to install 15.10.

If, however, you choose to remain with 15.04, you can compile the later driver. With a temporary working internet connection, by ethernet, tethered or whatever means possible, open a terminal and do:

sudo apt-get update
sudo apt-get install linux-headers-generic build-essential
cd ~
wget https://www.kernel.org/pub/linux/kernel/projects/backports/2015/11/20/backports-20151120.tar.gz
tar -zxvf backports-20151120.tar.gz
cd ~/backports-20151120
make defconfig-ath10k
make
sudo make install

Reboot and let us see:

dmesg | grep ath

This will tell us which firmware is missing and I will amend my answer to show how to download and install it.