How can I avoid kernel updates?

These lines are irrelevant to kernel upgrades. And also that is not good to comment them. You will not be able to install some packages if you do it.

You can freeze any package including kernel packages by

sudo apt-mark hold <package_name>

for example

sudo apt-mark hold linux-image-generic linux-headers-generic

But you need to check which kernel meta-package is installed for LTS versions. It may be linux-generic-lts-utopic, etc.