Does our 2009 Citroen Dispatch need an oil change?

I have a 2009 Citroen Dispatch 1.6-litre turbo diesel van. It's not yet due for a service on its factory oil (less than 500 miles). One of the staff topped up the oil with mineral oil 15/40 grade CC (as used in marine engines in our boats). Do we need to change the oil PDQ, or just get some proper semi-synthetic for future top-ups?
It's fairly close to needing a service anyway, so you might as well get that done.
Answered by Honest John on

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