This article analyzes the challenges of using traditional software process improvement (SPI) models in agile development contexts. Through a rapid literature review, 15 primary studies were selected to identify which traditional models have been used (e.g., CMMI, SPICE, MoProSoft) and the barriers they face when integrated with agile practices. The review concludes that while evidence exists supporting model use, their integration remains complex, particularly regarding organizational culture, training, and adaptation of processes to agile frameworks like Scrum.