Here are my thoughts, and why I did NOT buy 4115-but rather the 4110.
-The 4115 only added a few more ponies under the hood, but it was Direct Injected vs. the Normally Aspirated engine in my 4110.
-The length (wheelbase) was slightly longer, the only benefit was to allow the use of the 72" MMM
-The hydraulic system and capacities where identical to each other-both have dual pumps, and operated at the same pressure and GPM.
-The cost was over 3k difference at the time I think when I bought my 4110, and there was just no benefit for all that extra money.
Now, you'd have to compare the 2320 and the 2520.
-2320 has single hydraulic pump, 2520 has two
-2520 has bigger tires
-2520 has greater lift capacity
And that is just a few of the difference's.