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\section{Abstract}  We present ProCS15: a program that computes the isotropic chemical shielding values of backbone atoms and C$/beta$ C$\beta$  given a protein structure in less than a second. ProCS15 is parameterized based on on ca 2.35 million OPBE/6-31G(d,p)//PM6 calculations on tripeptides and small structural models of hydrogen-bonding. The ProCS15-predicted chemical shielding values are compared to experimentally measured chemical shifts for ubiquitin and Proteins G through linear regression and yield RMSD values of up to 2.4, 0.7, and 4.7 ppm for carbon, hydrogen, and nitrogen atoms. These RMSD values are very similar to corresponding RMSD values computed using OPBE/6-31G(d,p) for the two proteins. These maximum RMSD values can be reduced to 1.7, 0.5, and 3.5 ppm for carbon, hydrogen, and nitrogen by using an NMR-derived structural ensembles of ubiquitin (2KOX). The corresponding RMSD values predicted by several empirical chemical shift predictors range between 0.7 - 1.1, 0.2 - 0.4, and 1.8 - 2.8 ppm for carbon, hydrogen, and nitrogen atoms, respectively.