The 130 will have a 6 speed gearbox whereas the 115 will only have a 5 speed. 5th on the 6speed box is a better towing ratio on the motorway than 5th on the 5 speed.
I think the Mondeo towing limit is 1500kg, so you pretty close to the max capacity of the car with that van.
The main difference as Glenn has said is the gearbox. The 115bhp version has plenty of power for towing any caravan that is legal weight wise. My car is the 115 and to be honest I can use 5th while on the M-Way and decent A-roads without any problem. Sure get a 130 of it is available, but don't pay any extra for it. The best mark 3 Mondeo diesel for towing is the older 2.0l TDDI. This engine is also rtated at 115bhp, but solo is matches the 130bhp TDci 0-60 etc. It is also a more reliable engine and I notice very little extra refinement in the TDci (I have owned both). Of course it would be hard to find a fresh example with the TDDI engine now.
I have a 130bhp estate and it pulls like a train, but 6th gear is best over 70mph solo, and useless at 60mph towing. I always tow in 5th at around 2100rpm at true 60mph, and rarely have to drop to 4th.
I used to own a Mondeo estate 130bhp and all I can say about it is that it pulled our caravan (1250kg) as if it wasn't there. Unfortunatley I found the Mondeo the most uncomfortable car ever so had to get rid of it, but cetainly a great tow car.
My wife has a 51 plate 115hp hatchback with 96000 on the clock. It averages 48mpg overall and I have had 60mpg on a long motorway stint (tank-tank) (around 65mph by satnav). The torque comes in quickly and its not the quitest of motors but when we hooked up the 1400kg van for a trip it towed okay and was stable, but we don't use it to tow now as the towbar is off and we have a Sorento. The top gear being 5th was quite okay when towing and gave good pull on M ways for overtaking.
if u can afford it and can find one get the 2.2 version. the tddi is pants. i tow a coachaman amara 580/4 1560 kg with a 130 6 speed tdci.and get 30 mpg. only buy with history and check bills to see what has been done the earlier 130 also had a choice of 5 or 6 speed boxes.