Increasing Discount rate increases /decrease Interest cost ?

CFA Level II FRA
#1

THe swchezer says : Increasing discount rate will usually reduce Interest cost ( PBO * Discount rate).

Can anyone help explain why? From my understsanding there are 2 effects here:

-Increasing discount rate will increase interest cost (1)

-Increasing discount rate will lower PBO (2)

Normally the (2) effect will be more profound ( for plan that is not mature yet), thus Interest cost is reduced.

Am I getting it right ?

How can we know if the plan is mature or not?

#2

Not sure about the maturity part but the way I understood it was: 1) Increasing discount rate will not increase interest cost. This is because 2) Increasing the discount rate will decrease the PBO. The service cost is a PV amount and is included in the PBO. The higher the interest rate the lower this PV number is. Even though you multiply the PBO with a higher discount rate, that PBO is lower than it was pre-interest rate increase.