black or crome rims??? or Over size tires?
I'd say do whatever you want it to look like. A frontier with big tires, rims, etc., looks awsome!!!! If choosing between the two, I'd get the rims. but that's me. Snzip
14 Rims and tires may be able to work. can result in a variety of issues as people have already noted. Though if the total diameter of the 14 set is very close to the 15 set, it will make very little difference aside from most likely having less mass and a softer ride. Now, one key issue not mentioned: Brakes! You need to find out if a 14 wheel will fit over your brakes. If not, then 15 is the smallest you can use and the 14s will not work. You don't mention the year of the Sentra, so I am not sure what the OE options were, but if there was a 14 option from the factory, then you should be ok.
Larger tires less gas milage. Go online with Tire Rack Dot Com and look at what your truck will look like with different wheel and tire combinations.