Hello Clarencelzj
Thank you for your kind words. That’s the aim of the SBB Community: to clarify questions.
Yes, you are welcome to purchase the class upgrade at half fare, thus CHF 12 is the correct price.
I see that you want to travel on 12 May, which is Mother’s Day here in Switzerland. On a day with great weather, the Luzern-Interlaken Express is very busy in the morning, you have to expect many people doing an excursion as part of the Mother’s Day celebrations.
What time do you intend to travel? As there might be many travellers on that day, a seat reservation would be a good investment, especially if you wish to travel in the morning. You can get it from here:
https://store.luzern.com/luzern_en/specials/daytrips/zentralbahn-int-lu
Are you keen to know an expert tip? Choose a seat on the right-hand side in travel direction, it offers much better views than the left-hand side.
Please let us know how the journey went, especially if the train was fully booked; it helps us to give better advice to fellow travellers based on your experience.
Best wishes,
Roland
@RomanoS @Sarah_W