It says you don't get level 6 spells until level 28. Since I am building my paladin with 4 levels of fighter, I am thinking it isn't worth giving him more than a 14 or 15 wisdom, assuming this chart is correct.

I believe it is correct. Still, I've found that the magic number for a paladin's WIS is... 11. WIS increasing items are in abundance. If you want, you can take 12 for Draw Upon Holy Might, but after that its nothing that a cleric can't do better.

Cool. Thanks a lot, Marty4. This will help me make my Paladin a better fighter-type character, as I've been picturing him with a 14 (since I know there is a +1 WIS ring I can buy in the Prologue).