@Tjaart: As far as I am aware the 4500GRX should be able to take 15" rims. The problem comes only with the 4.8, which has larger front brake calipers (too large for a 15" rim to clear).
The best bet is to go past TWT or one of the other rim retailers and pull a front and rear wheel off, and see if they have a 15" that will fit.
On my 1998 4.2TD, a 15x8" rim with a -0.25PCD works very well in combination with 33x12.5x15MT`s. The steel rims that I bought are commonly used by the Hilux and Cruiser crowd as well. I paid about R450 per rim.
Good luck!
. Now the long search for mags/rims begins. Luckily, I'm not in a hurry and the Maxxis got a lot left in them!!! Please, 
, if any knows about mags or rims somewhere, let me know!! 
Damnit. Het jy dalk 15" rims? 
....do you have a conection or did you just get lucky on a good deal?
. That also helped my decision to change to 15" tires. They are cheaper than 16", freely available and looks better on nice rims. I am just battling in this back-water hell hole aka[k] Polokwane to get rims. 
. What size are your tires?