Shin Megami Tensei V: Vengeance has a lot of additional content that builds on its 2021 predecessor. This new content and the additional storylines give it a very different runtime.
Shin Megami Tensei V: Vengeance First Impressions
There are now two primary story paths in the game: Canon of Creation and Canon of Vengeance. These paths will further split based on decisions you make later in the game, but the important thing to note is that the time it takes to beat Shin Megami Tensei V: Vengeance is essentially the same regardless of your chosen path.
The original Shin Megami Tensei V was around 60-80 hours long if you just played the main story and ignored most of the side content. Playtime went up to 100-120 hours with side content and DLC additions.
Shin Megami Tensei V: Vengeance adds 75 hours of new content to the game, including a new story path and plenty of new bosses. That brings the total time to beat SMT V Vengeance if you play side content to 175-200 hours, and the time to beat it without focusing on side content is still around 80 hours. Definitely a good buy if you want something to play for a long time.