Ah yes, for those that haven't travelled in these sort of trains (AVE from RENFE): there are practically no "major" differences between 1st and 2nd class. While seats are indeed larger and more comfy in 1st -hence fewer people per carriage- 2nd class carriages are extremely comfortable too (https://www.youtube.com/watch?v=Zu5r_hGJDoo) and, despite carrying more people, they're very quiet.
FURTHERMORE, there are special carriages in many AVE lines called "MUTE carriages" which you can choose when booking. They cost the same than the other carriages but those travelling in these agree to follow certain rules: phones must be muted and silence is the norm (no conversations), if you want to listen to music it must be done on a low volume and, obviously, with headphones. These are great if you intend to work on route.
PS on a side note, the nomenclature we use here is rather far less discriminatory: we call them "clase Preferente" and "clase Turista" instead. https://www.renfe.com/es/es/viajar/el-viaje/a-bordo/clases