Krikor wrote: Not too many. Mostly minor visual edits, a new itemform.php layout, but if you are using overrides the update will not affect you.

However, to be extra safe you should backup prior to the update.

We do daily backups of both database and root folder with all content so that wont be a problem. I have overridden the files right in k2 component, not in template/html folder.

I read somewhere that joomla has increased in speed, is this correct? Somewhere it said 2x but thats too good to be true.

The overrides is an issue. The right way is to put them in your template's html folder.

Supposedly with PHP7 it is blazingly fast.
To be honest, Joomla! sites with a solid server setup were already fast.