Cascaded random Raman fiber lasers (CRRFLs) with simple configuration and high spectral purity have become a great candidate for power scaling over the 1.1 µm-2 µm spectral band. Recently, CRRFLs with high spectral purity over 90% have been proposed by applying a highly temporal-stable pump source or a free-space short-pass filter, at the cost of increased system complexity. In this work, pumped directly by a Yb-doped fiber oscillator at 1080 nm, an all-fiberized and simplified CRRFL with a short-pass optical filter based on bending fiber and a thin-film wavelength division multiplexer is demonstrated. The transmission loss of the filter for 5th Stokes order at 1440 nm is up to 70 dB. Spectral purity over 92% for all the first four Stokes orders is achieved. The highest output power is 15 W for the 4th Stokes order at 1341 nm.