Hi,
after I updated to PHP7 on a Raspbian Jessie installation with some trouble I want to share my experience on that workflow. My Server runs NC12.0.4 and a MySQL DB.
First of all I wanted to follow this thread to install.
But for Raspbian the DotDeb repository didn’t work. 
After doing some search it was clear why. DotDeb offers only x86 and x86-64 architectures packages and not ARM. So I found this side with good infos on raspbian php7 install and the hint to Matis repository
What I have done to succeed was following:
Add the new repository for jessie in an extra file in /etc/apt/sources.list.d named mati75.list
deb http://repozytorium.mati75.eu/raspbian jessie main contrib non-free
#deb-src http://repozytorium.mati75.eu/raspbian jessie main contrib non-free
Add the keys for the repository
gpg --keyserver pgpkeys.mit.edu --recv-key CCD91D6111A06851
gpg --armor --export CCD91D6111A06851 | apt-key add -
Run APT Update
apt-get update
Install PHP7
apt-get install php7.0 php7.0-opcache php7.0-apcu php7.0-curl php7.0-gd php7.0-mcrypt php7.0-mysql php7.0-mbstring php7.0-phpdbg
Disable PHP5 and enable PHP7
a2dismod php5
a2enmod php7.0
service apache2 restart
Hope this helps other to do the upgrade to PHP7.
Cheers!