A high-powered millijoule pulse energy Tm3+-doped fiber amplifier seeded with a Q-switched operation of Tm (4 at.-%), Ho (0.4 at.-%):YVO4 laser is reported. The output characteristics of the amplified laser are studied at the coupled powers of 0.266, 1.24, and 2.65 W. Maximum output power up to 15.7 W is at 10-kHz repetition rate. Nonlinear effects are not observed from the emitting spectrum and the full-width at half-maximum (FWHM) of the pulse duration is reduced from 40.1 to 25.9 ns at 1.57-mJ pulse energy. The beam quality factor M2x=1.9\pm 0.03, M2y=2.1\pm 0.02 at the output power of 14.5 W is measured using the traveling knife-edge method.