There is another option, but you would need to “do the math” a bit to see how the costs compare. This involves predicting which mountain lifts you may want to ride, plus looking up the cost of various train journeys.
That is to buy the 6-day Berner Oberland Pass and a Half Fare Card. The price for the BO Pass with a HFC drops from 350 CHF to 254. That comes close to covering the 120 CHF cost of the Half Fare Card.
The HFC is good for 30 days, so will cover your whole trip, reducing the travel cost from Basel (where you enter Switzerland) to Zermatt, and from Zermatt to Spiez or Brig (where the BO Pass kicks in). *** The BO pass will then fully cover your recreational lifts and train travel for 6 days (two exceptions already noted), as well as the train trip to Luzern on Day 6 of the pass. After that, the Half Fare card will cover 50% of everything—-boats, trains, and recreational lifts—-for the rest of your time in Switzerland.
***I said Spiez or Brig because the BO Pass will cover the journey from Brig if you take the regional train via Kandersteg instead of the deep Lötschberg Basistunnel from Visp to Spiez. You can see the two routes on the Swiss rail map:
https://www.swiss-pass.ch/wp-content/uploads/pdf/swiss-travel-system-map.pdf
The tunnel is shown in the dark dashed line starting at Visp. To take the regional train, you go from Zermatt past Visp to Brig, and board a regional train there. There is still a tunnel—-see the lighter dashed line from Goppenstein to Kandersteg—-but this route is covered on the BO Pass, as you can see on this map of validity:
https://www.berneseoberlandpass.ch/assets/Uploads/BLS-BO-Pass-M-24-WEB-komprimiert_compressed.pdf
You will see that same switchback in the track just north of Kandersteg.
This option (BO pass with Half Fare Card) would cost you 374 CHF and might be cheaper overall than the 15-day Swiss Pass IF you plan to ride a number of the recreational lifts in the BO, you take the slower route via Kandersteg when traveling from Zermatt to Wengen, AND you do not have a lot of expensive train, boat, and lift rides planned during your Luzern time. (Remember that the Swiss Pass will fully cover the faster Visp-Spiez route to Wengen, plus boat and regular train rides at Luzern, such as to Engelberg and back).
If you do choose this BO plus HFC option and plan on doing the Rigi round trip, consider getting a Saver Day Pass (using your Half Fare Card) for one day to cover that—-but then you are committed to that day, regardless of weather.
Also note that with this BO + HFC option, once you are outside the BO pass validity region, you lose the convenience factor of a travel pass—-you will need to buy tickets for each journey before boarding the train.