A high-end VR headset is an investment in your fitness and gaming setup. Buy the right one now and it will last you for years, saving you from needing an upgrade before the next major hardware shift.
Tech companies refresh these models on a cycle. Wait for the big holiday sales to buy, as that is when you can grab last year's flagship model for much less than the newest release.
That 15-month window is a deadline, not a pass to pay forever. If you still have a balance once the 15 months are up, the interest rate will jump up and you will start paying extra on whatever is left.