The application effectiveness of traditional optical parametric amplification systems has long been limited by the performance of the driving source. To address this issue, a high-power mid-IR optical parametric amplifier is demonstrated using a 1.5 μm all-polarization-maintaining erbium-doped fiber master oscillator power amplifier (MOPA) system. The OPA is seeded by a 3.27 μm continuous-wave (CW) interband cascade laser, where the femtosecond pump pulses perform nonlinear slicing and efficient amplification of the CW seed within a periodically poled lithium niobate crystal. Experimental results demonstrate that at a pump power of 4.6 W, the system delivers mid-IR femtosecond pulses centered at 3.25 μm with a spectral bandwidth of 36.4 nm and a maximum average power of up to 440 mW. Notably, the 1.5 μm pumping scheme employed in this work fundamentally circumvents the bottlenecks of parasitic visible absorption and severe thermal lensing inherently suffered by traditional 1 μm pumped architectures. Benefiting from this exceptional immunity to thermal damage and a higher quantum efficiency limit, massive parametric gain is successfully extracted by utilizing a long nonlinear crystal. Furthermore, radio-frequency spectral analysis reveals a signal-to-noise ratio exceeding 50 dB at the fundamental frequency, confirming that the system maintains superior time-frequency stability alongside its high-power performance. This architecture offers a highly scalable and robust technical paradigm for the development of compact, high-power mid-infrared femtosecond sources.