Three sides to the issue: First, how heavy is it vs. size of your tractor; second, how much hp do you need to run the thing; third, how wide is the tire track vs. the tiller.
An
L2500 weighs something like 2700lbs, so it should be able to handle a 5ft tiller with no problem, maybe even a 6ft, weightwise. But it only has 22.5 pto hp, which is a bit low for a 6ft. and you'd probably do better with a 5ft.
This also depends on what kind of soil you have... sandy soil needs less power than heavy, moist clay, for example.
Regarding tire width, you'll have to measure your
L2500. Many tillers can be offset some left or right, so even if the tractor is wider than, say 60", you can still use a 5ft tiller by shifting it to one side and making overlapping passes.