Dpf issues?

Afternoon, I have a MK2 VRS TDI estate, in the last few wks I have noticed that when my car is doing it's regen it's taking a lot longer to do. It used to take around 30-40 miles to complete but now it's taking around 60 miles the car has done 155000 near as and to my knowledge still on original dpf, I'm starting to think maybe the dpf is on the way out? I know it can depend on weather conditions etc as well, I don't tend to drive it in 4th gear at 2500 rpm I just drive it at 60-70mph in 6th which normally works for it. Just wondering if anybody has had same kinda problems at all please?