I had the same experience this last weekend. I also have a 2005 X Off Road 4WD manual transmission with the Nevada towing package and had the same problem.
The reason I bought this car was because with an Off Road and a tow package, my belief was that the suspension would be stronger.
My problem ... four adults and carry on luggage in the trunk and my X is bottoming out on the freeway.
I also checked the distance between the top of the rear axel housing and the rubber stop and was close to 1.5" just like you.
Something must be wrong. I measured the car unloaded and the distance betweeen the rear axle housing and the rubber stop was 2.5".
May be Nissan is trying to give customers a mini van ride on an off road machine.
What are the solutions to this problem? Is the suspension that wimpy? Is the suspension adjustable?
I thought that I purchased an off road car. I did not buy the off road package to go down the street to the supermarket.
Possible solutions:
DETAILS:
1. Longer Rear Shackles. Stock 4" to 6" which will provide more clearance.
2. Cut 1" Off the axle stop
3. Air shocks instead of Bielstein
4. Add a leaf
5. Unloaded clearance between the axle stop & the axle housing is 2.5"
I would like to hear about solutions to this issue.