I got these values from the tables on NWN Wiki
Excluding cantrips, spell progression as a level 15 clr should be:
6 6 6 5 5 4 3 2
+ bonus spells for 18-19 ability modifier
1 1 1 1
- 1 slot per spell level house rule =
6 6 6 5 4 3 2 1
but I have
6 6 5 5 4 3 2 1
So I seem to be missing one 3rd level slot, or is there an additional reduction somewhere I didn't see?