How can I lower my truck with smaller 15 inch tires?

Thanks, tenisshoes, but I'm not wanting to turn my little truck into a low rider. I'd just like to drop the height down a few inches. I'm a pretty short, older guy (5'-6"), had back surgery last year, and now have to climb up a little into the cab. What I'd like is to get the level down, so I can just back up to the seat and basically just turn around and be seated? I was considering maybe dropping down to maybe a 20570R15 or 21570R15?

That sounds great! Thank you so much!