Prethermalization refers to the relaxation to a quasistationary state before reaching thermal equilibrium. Recently, it was found that not only local conserved quantities but also entanglement plays a key role in a special type of prethermalization, which we refer to as entanglement prethermalization. Here, we show that in the Tomonaga-Luttinger model entanglement prethermalization can also be explained by the conventional prethermalization of two independent subsystems without entanglement. Moreover, it is argued that prethermalization in the Tomonaga-Luttinger model is essentially different from entanglement prethermalization in the Lieb-Liniger model because of the different types of energy degeneracies.