Not only should you drive one, but do it at a Land Rover dealer and let them take you over the obstacle course. My local dealer (Utah) had Rubicons on the course to, so you can compare both. (Sadly, due to the sue-happy environment which is our country, only the salesmen can go over the course); but, you will get an idea of the pros and cons, and especially comfort of the vehicle.
I was(am) in a similar boat as you. My wife likes to come, but she has a hurt back, and solid axle, short-wheelbase rigs are horrendous over corrugated roads! Right now I have a D2 which she likes, but it could be better. We were thinking of taking the depreciation hit on our 2011 2500HD truck and trade it in on an LR4/RRS/or L322 (thanks overland journal and expo for all the info on modifying these things).
driving them back to back, the LR4 was nice, don't get me wrong, but it didn't compare to the rangies overall (unless you wanted the LOOK and the CARGO space.) it's ride, while excellent, wasn't nearly as taut and just "felt" heavier.
I liked the RRS because of the shorter wheelbase and I love Chris' build and thinks it looks fantastic. Instantly, my wife hated the seats. It's a sports-ute, let's face it, and resembled my old 540i on the highway yet had more out of the box performance than my D2.
Finally, the L322 (which we actually drove first). It was a late model, jag engine and TFT screens. Holy crap, now I know how the "other side" lives that can afford $90~120k cars new. The thing was awesome AND comfortable. It helped my wife's back out the best, and had superior off-road performance out of the box (I know the LR4 is more easily modified), and was the best on the highway.
It was simply outstanding. We decided on the L322 and went to another dealer that had the lux-package with surround view camera (another fun toy for those impossible-to-see approaches). We almost bought it, but it only had 1 remote and the Caddy dealer we were at wasn't interested in buying and programming a 2nd for us.
When they finally agreed, I ran the numbers you were running: I figured that if I waited 3 years to pay off the 2500HD, the depreciation on the 2011/2012 L322s would be such that they'd probably have 30k more miles, but be $20k LESS in price. If I just waited 3 years I could KEEP the 2500HD and get the L322 I wanted in exchange for $3-5k cash and 30k miles. It was a no brainer for me, so we are enjoying the disco and waiting for the truck to be paid off.
Now you have a 2015, so that's a bit more debt load than I do, but something to think about. In your favor, well modded rubi's seem to hardly lose their value, so you won't take quite the hit I was going to take.
In short, I grew up a Jeep guy. I've owned 2 ZJs, grew up with a CJ7 and drove many TJs, all of these Jeeps I've taken over excellent courses in Moab, so I know them pretty well (except the new IFS rigs).
I've found that I just like LR. The D2 feels like driving a TJ (thank's to 100" wheelbase) with the comfort of a ZJ grand and the "coolness" factor that no Jeep can attain to. It makes the maintenance worth it.
The L322/RRS/LR4, which I've ignored for so long due to the IFS/IRS, are just works of art. The cross-linked air suspension is the real deal, and these things can do some serious trails with just some tire mods and skid plates. And not only that, but they defy their weight on the highway and feel more like a plush sedan. The only thing I can compare all 3 to is that they are more like my old '02 BMW 540i Sport on the highway, and not even near the feel of the Tahoe/Suburban/Cherokees and other SUVs I've driven in the past. Off-road, they are in their own league and something you really can't compare to anything else.....again, making the maintenance worth it.
Anyway, I apologize for the long post. Take your time. Make a date with you and your wife and drive all 3 offerings. Don't trade in the JKU, you'll do better selling it privately. Get a LR, mod it, take it to some cool destinations and send us lots of photos!