just some FYI Diesel oil, maintenance information:
oil STJLR.03.5007 pt#15CB3E (12090) 0w-30 (C2)
engine oil:
Ravenol FES 0w-30
Castrol (Pro E) edge 0w-30
Valvoline European Formula full synthetic 0W-30
Motul Synthetic Engine Oil 8100 0W30 ECO-Clean

It is sometimes hard to find oil that meets the diesel engine engine engine specifications.
Even though all the above oil meet the JLR specification, there are advantages and disadvantages to each brand believe it or not.
Castrol has unstable viscosity and is most susceptible to fuel dilution problems.(Viscosity at 100 °C (cSt) 9.5 quietly updated to 9.8)
Ravenol is actually POE not Hydro-Crack and has the best oil properties, including more stable viscosity rating (Viscosity at 100 °C (cSt) 9.4)
Valvoline Believe it or not is a quality product and has the highest viscosity rating (Viscosity at 100 °C (cSt) 12.3) best for both fuel dilution, and higher ambient temperature driving.

 

I've been using non-JLR specs oil but I'm doing OCI every 5K miles for my XF. Currently it has Valvoline EP 0W-20 Synthetic. And my Land Rover as well (Quaker State 0w-30 Synthetic High Mileage)

 

Forget what I wrote, I just remembered you don't have the diesel Jags.

 

Just using non-specification oil or not isn't necessarily better or worse. Engines, not just JLR, do sometimes need specific requirements in the oil.
Even just the wrong amount of calcium can cause piston damage in Direct injection gasoline engines over time. Some additives can damage catalytic converters if you have one.
Timing chains now have special additives required in the oil to reduce internal friction and failure. Every oil has a specific range of use and there's a difference between older engines and newer engines.
There's nothing wrong with using an out of spec oil if it can still fill all the needs required for the specific engine and not just a guess.
Oil change interval is based on conditions and oil sampling. Under normal condition conditions 7500mi oil change would be considered normal.
Under most conditions, 5000 miles is just a waste of oil if the oil sampling shows the oil is in good condition still.
There's also one other limiting factor. Generally conventional oil breaks down much faster than synthetic oil. The original 3000 to 5000 mile oil changes on the older engines was due to the lower quality of additives and the oil breaking down rather quickly. Synthetic oil changed everything so old-school thinking no longer applies.