The performance of the missing transverse momentum ( Formula omitted) reconstruction with the ATLAS detector is evaluated using data collected in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV in 2015. To reconstruct Formula omitted, fully calibrated electrons, muons, photons, hadronically decaying Formula omitted, and jets reconstructed from calorimeter energy deposits and charged-particle tracks are used. These are combined with the soft hadronic activity measured by reconstructed charged-particle tracks not associated with the hard objects. Possible double counting of contributions from reconstructed charged-particle tracks from the inner detector, energy deposits in the calorimeter, and reconstructed muons from the muon spectrometer is avoided by applying a signal ambiguity resolution procedure which rejects already used signals when combining the various Formula omitted contributions. The individual terms as well as the overall reconstructed Formula omitted are evaluated with various performance metrics for scale (linearity), resolution, and sensitivity to the data-taking conditions. The method developed to determine the systematic uncertainties of the Formula omitted scale and resolution is discussed. Results are shown based on the full 2015 data sample corresponding to an integrated luminosity of Formula omitted.