I run 275/55/19's and there are two problems that I think you will encounter with 285/55/19. First, a full size spare will not fit under the vehicle. In order to fit the 275/55/19, it needs to be deflated to about 15 pounds and even then needs some wiggling and kicking to fit. Second problem is that you will just about turn the LR 3 six speed auto into a five speed as it will rarely shift into top gear with the loss of gearing. You will never see 6th gear if you switch to sport mode or pull a trailer.
I think the tire will fit the rim and the wheel wells but consider the other issues before you commit.