Somewhere between 3,001 and 15,000 hrs. It is more a matter of what shape the engines are in and how they have been used and maintained rather than a specific number of hours for a specific brand/model.
How are they running now? Oil pressure, compression
, temperature, oil consumption
, smoke, etc?
If in excellent shape, maintained well and used judiciously, they should have another 3000 in them with some basic stuff like rebuilding the injectors and new exhaust
Or they could go tango uniform tomorrow.