Koh is limiting both sides invalidity arguments (arguments made why the other company's patents are invalid) to 15. If each side were to claim that the other infringed on 5 patents for example, that would allow both firms to give three reasons why each patent is invalid. Judge Koh has limited the trial to 12 days which means that eventually we will see limits on the number of expert witnesses each side can present, and a limit on the amount of time that a witness can be questioned on the stand. This is nothing new as both sides faced similar limits during the first trial, which ended in a jury awarding Apple a huge award. Samsung is currently appealing the decision.
In December, Judge Koh will start making her summary judgment rulings which would leave either side with fewer patents to argue about. In a previous order, Koh ruled that for the summary judgment hearing each side would be limited to 10 claims from 5 patents. After the summary judgment rulings are made, starting on February 6th, each side would be limited to 5 claims for the actual trial.