How to Remove Snap from Ubuntu

First some clarification : qemu is a metapackage, depending on all other qemu-related packages.
As I use the synaptic package management tool which has the possibility to save the complete installation history of all time, I am able to tell you which packages are installed alongside qemu.

Commit Log for Thu Apr 21 18:34:38 2016  

Installed the following packages:  

cpu-checker (0.7-0ubuntu7)  
ipxe-qemu (1.0.0+git-20150424.a25a16d-1ubuntu1)  
libaio1 (0.3.110-2)  
libboost-random1.58.0 (1.58.0+dfsg-5ubuntu3)  
libboost-thread1.58.0 (1.58.0+dfsg-5ubuntu3)  
libcacard0 (1:2.5.0-2)  
libfdt1 (1.4.0+dfsg-2)  
libiscsi2 (1.12.0-2)  
librados2 (10.1.2-0ubuntu1)  
librbd1 (10.1.2-0ubuntu1)  
libspice-server1 (0.12.6-4)  
libusbredirparser1 (0.7.1-1)  
libxen-4.6 (4.6.0-1ubuntu4)  
libxenstore3.0 (4.6.0-1ubuntu4)  
msr-tools (1.3-2)  
qemu (1:2.5+dfsg-5ubuntu10)  
qemu-block-extra (1:2.5+dfsg-5ubuntu10)  
qemu-slof (20151103+dfsg-1ubuntu1)  
qemu-system (1:2.5+dfsg-5ubuntu10)  
qemu-system-arm (1:2.5+dfsg-5ubuntu10)  
qemu-system-common (1:2.5+dfsg-5ubuntu10)  
qemu-system-mips (1:2.5+dfsg-5ubuntu10)  
qemu-system-misc (1:2.5+dfsg-5ubuntu10)  
qemu-system-ppc (1:2.5+dfsg-5ubuntu10)  
qemu-system-sparc (1:2.5+dfsg-5ubuntu10)  
qemu-system-x86 (1:2.5+dfsg-5ubuntu10)  
qemu-user (1:2.5+dfsg-5ubuntu10)  
qemu-user-binfmt (1:2.5+dfsg-5ubuntu10)  
qemu-utils (1:2.5+dfsg-5ubuntu10)  
seabios (1.8.2-1ubuntu1)  
sharutils (1:4.15.2-1)

To remove all the qemu related packages - open a terminal and execute the following command :

sudo apt-get purge cpu-checker ipxe-qemu libaio1 libboost-random1.58.0 libboost-thread1.58.0 libcacard0 libfdt1 libiscsi2 librados2 librbd1 libspice-server1 libusbredirparser1 libxen-4.6 libxenstore3.0 msr-tools qemu qemu-block-extra qemu-slof qemu-system qemu-system-arm qemu-system-common qemu-system-mips qemu-system-misc qemu-system-ppc qemu-system-sparc qemu-system-x86 qemu-user qemu-user-binfmt qemu-utils seabios sharutils  

Note : This is from Ubuntu 16.04 - in case that a single package (example : libboost-random1.58.0) has a different name in Ubuntu 15.10 you can check this with dpkg --get-selections. But most packages should have the same name ... now you have completely removed every trace of qemu.

I have checked the packages for wilyon packages.ubuntu.com and I found one package with a different name : libxen-4.6 which in wily is libxen-4.5 - so you have to replace this in the purge command. You also may consider to keep the lib packages, just to be on the safe side.

Update addressing your comment that you still have a not running qemu-kvm service listed :

This is a startup service which is running when you additionally installed the qemu-kvm package.

You have two options, you can disable the service with systemctl disable qemu-kvm or you can remove the service with sudo rm /etc/init.d/qemu-kvm. To also remove the configuration file, execute sudo rm /etc/init/qemu-kvm.conf. Now reboot the system - the service will be gone.

I can share the results of some experimenting with two versions of LibreOffice 6.1.3.2: one as a snap delivered with ubuntu 18.04 and another one installed from the official ppa. Please keep in mind the values I give below are approximate.

Startup time of an empty Calc spreadsheet

• ppa: 1.5 s

• snap: 13 s

Conversion time of 13-slides (mostly png pictures) to pdf with impress

• ppa: 9 s

• snap ~70 s

Disk usage [MB] (expected / real)

• ppa: 369 / 483

• snap: 507 / 1269

I realize these values depend on the hardware and specific configuration of the system I'm using. However, considering I have used the same laptop, operating system and LibreOffice versions, I believe relative comparison is still informative.

Altogether, on my laptop snap image occupies more than 2 times the disk space and it is almost 10 times slower than the corresponding ppa. In contrast with common opinions subsequent startups of snap application are not faster on my system.

My personal view on the end-user's benefits of snap is related only to system security (no sudo required to install, limited runtime permissions). So if you're running a personal system at low risk, I'd stick to ppa's. In such cases the enhanced security is not worth the cost of much worse performance in the present-day snaps.