Many people have run 15's, but the one guy with the Nissan wheels is the first problem ive heard of. Must be an offset related issue?
Besides looks, wheel size is summed up really easy. smaller wheels normally decrease rotational mass, unsprung weight, increase mpg (not including 8 ply or heavy treading)etc. Which is better for acceleration and offroad setups due to more rubber between wheel and ground). Larger wheels increase rotational mass and unsprung weight, but improve steering response. Also the "bling factor" hahahaha. At least in recent years offroad tires are made in all wheel sizes. Prior to the last 10 years, almost nothing offroad was for 16"+. Due to rough roads, unexpected VX usage in extreme weather, occasional farm duty, cost, availability, my stock 16" wheels with MT's have never let me down.
Have you ever thought of just getting some 16" stockers, and just switching on/ off road wheel setups based on your own whim and a 15 minutes with a wrench?
For lifts, do the suspension. Body lifts are great for a few inches, but there are better mechanical advantages to suspension lifts. Besides, for our rigs, they are cheap and easy. How can you beat that even when the performance is better vs. a body lift?