We present a parametric component separation forecast for the QUIJOTE─MFI2 instrument (10─20 GHz) that assesses its impact on constraining polarised synchrotron emission at 1° full width at half maximum and Nside = 64. Using simulated sky maps based on power-law and curved synchrotron spectra, we show that adding QUIJOTE-MFI2 to existing WMAP+Planck+MFI data yields statistically unbiased parameter estimates with substantial uncertainty reductions. The improvement factors reach ∼10 for the synchrotron spectral index (βs), ∼5 for the curvature parameter (Cs), and ∼43 for polarisation amplitudes in bright regions. Deep QUIJOTE cosmological fields enable βs constraints even in intrinsically low S/N regions, where WMAP+Planck alone remain prior-dominated. Current combined sensitivities are insufficient to detect a synchrotron curvature of Cs = −0.052 on a pixel-by-pixel basis, but a 2σ detection is achievable for |Cs|≳0.14 in the brightest regions of the Galactic plane. In those deep cosmological fields, combining QUIJOTE-MFI2 with WMAP and Planck reduces the median synchrotron residual at 100 GHz by a factor of six to 0.033 μ KCMB. These results demonstrate that QUIJOTE-MFI2 will provide critical low-frequency information for modelling Galactic synchrotron emission, therefore offering valuable complementary constraints for future cosmic microwave background surveys such as LiteBIRD and the Simons Observatory.