The "15-Minute City" (15mC)—an urban planning model where all essential human needs are met within a short walk or cycle—has been hailed as the ultimate solution for urban sustainability and well-being. However, as major metropolises from Paris to Seoul implement these frameworks, a "Proximity Paradox" has emerged. This paper investigates how the 15mC model potentially exacerbates socio-economic segregation by concentrating high-value amenities in already affluent districts, leading to "Green Gentrification." Using a comparative analysis of three "15-Minute" pilot projects in diverse global cities, we examine the correlation between "Walkability Scores" and real estate price surges. Our findings suggest that without aggressive "Inclusionary Zoning" and social housing mandates, the 15-minute model risks becoming an exclusive amenity for the elite, effectively "walling off" lower-income residents into 15-minute "service deserts." We propose a revised "Equity-First" framework for hyper-local urbanism that prioritizes cross-district connectivity and essential service distribution for marginalized populations.