It may seem to have gone 4 years without and oil change, but it was only 15K miles so maybe not a disaster.
And it's possible it did get an oil service that didn't get a stamp in the book. When I bought my E91 in March 2018 I found out it had been serviced at Barons in Hindhead the previous December, so I took the book over and got the stamp.
In any case it's only at £8K at the moment so a bargain for someone, although I think that will increase over the next 5 days.