The motivation of this study is to provide empirical evidence of service companies’ performance regarding nine dimensions in a total quality management model during the COVID-19 pandemic. The nine dimensions highlight strategic company activities, and it allows a comparative analysis of the overall effect of having a QMS such as ISO 9001:2015 on Peruvian service companies. A total of 630 Peruvian service companies were surveyed for this study. The questionnaire included 35 Likert-scale items that were further classified into nine (9) dimensions. The Mann-Whitney U test was used to estimate any significant differences between the ISO 9001 certified and non-certified companies. Our findings showed that the performance of ISO 9001:2015 certified companies was significantly higher than that of non-certified companies in all dimensions. Moreover, our findings showed that managers in ISO 9001:2015 certified companies effectively implemented the nine dimensions of the model. The originality of this study lies in proving the positive effect of having a QMS in service companies in a context of slow economic growth and decline of consumer demand such as the COVID-19 pandemic. The findings might encourage service companies, especially those in developing countries, to allocate the necessary resources to obtain a QMS such as the ISO 9001:2015.