Administrative delays in city governments undermine citizen satisfaction, economic performance, and governance effectiveness. This systematic review synthesizes evidence from 26 peer-reviewed studies published between 2015 and 2025, examining approaches to reduce service delays in municipal contexts. It focuses on four key methodologies: Lean and Six Sigma, Business Process Reengineering, digital transformation, and administrative simplification reforms. Findings show that structured improvement approaches consistently reduce service turnaround times, with the strongest effects observed in high-volume, routine administrative processes. Digital transformation proves particularly effective, though outcomes depend on service complexity, implementation quality, and contextual factors such as infrastructure and socioeconomic conditions. Critical success factors include sustained leadership commitment, stakeholder engagement, robust performance measurement, organizational capacity for continuous improvement, and careful adaptation of methods to public sector realities. Implementation barriers remain substantial, including organizational resistance, limited technical and managerial capacity, political dynamics, and resource constraints, which disproportionately affect smaller municipalities. Contextual factors such as municipal size, governance structures, and institutional legacies shape both feasibility and outcomes. Effective delay reduction requires integrated approaches combining multiple methodologies, aligned with local conditions, alongside investments in capacity and change management. The study informs public sector process improvement scholarship and provides actionable guidance for municipal administrators seeking efficient, accountable, and equitable service delivery.