Not sure whether the above mentioned fix has been committed yet or not but today's update-notifier-common update to version 3.163.1 which arrived via Kubuntu PPA did not fix the problem for me on my Kubuntu 15.10 system with Plasma 5.5.3: apt-get update command still spawns hundreds of rough apt-check processes which eat up all memory and CPU on my desktop.
Not sure whether the above mentioned fix has been committed yet or not but today's update- notifier- common update to version 3.163.1 which arrived via Kubuntu PPA did not fix the problem for me on my Kubuntu 15.10 system with Plasma 5.5.3: apt-get update command still spawns hundreds of rough apt-check processes which eat up all memory and CPU on my desktop.