The ATLAS Collaboration presented an overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC in 2015, focusing on the performance of the trigger system based on proton-proton collision data recorded at a center-of-mass energy of 13 TeV. The ATLAS trigger system is crucial for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. Key changes during the shutdown included upgrades to the Level-1 calorimeter and muon triggers, the addition of a new topological trigger (L1Topo), and improvements to the High-Level Trigger (HLT) system. The paper details the trigger menu, reconstruction algorithms, and performance of various trigger signatures, such as electrons, photons, muons, jets, and tau leptons. It also discusses the impact of increased luminosity and pile-up on trigger rates and the strategies employed to manage these challenges. The results show that the ATLAS trigger system effectively handled the higher rates and luminosities, with detailed analyses of trigger efficiency, reconstruction performance, and processing times.The ATLAS Collaboration presented an overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC in 2015, focusing on the performance of the trigger system based on proton-proton collision data recorded at a center-of-mass energy of 13 TeV. The ATLAS trigger system is crucial for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. Key changes during the shutdown included upgrades to the Level-1 calorimeter and muon triggers, the addition of a new topological trigger (L1Topo), and improvements to the High-Level Trigger (HLT) system. The paper details the trigger menu, reconstruction algorithms, and performance of various trigger signatures, such as electrons, photons, muons, jets, and tau leptons. It also discusses the impact of increased luminosity and pile-up on trigger rates and the strategies employed to manage these challenges. The results show that the ATLAS trigger system effectively handled the higher rates and luminosities, with detailed analyses of trigger efficiency, reconstruction performance, and processing times.