We present an experimental investigation of the Q-factor penalty due to intra and intermodal nonlinear signal distortions on 24.5 GBaud 16-quadratic-amplitude modulation based spatial super channel in a 36 km few-mode fiber. The results show that intermodal nonlinear signal degradations, caused by interfering spectral components separated by more than 17 nm, lead to similar Q-factor penalties as intramodal nonlinear signal degradations, originating in spectral components of less than 1 nm separation. We further compare the experimentally observed intra and intermodal nonlinear signal degradations with an analytical nonlinear Gaussian noise model and find a strong agreement between the two, validating the model as a computationally inexpensive tool for the design of few-mode fiber-based transmission systems.