a lot will depend on quality of oil filter, you cant see whats inside , so buying a comparable filter not major brand who knows.
heres whats inside and what they do, you can see differences in internals that could lead to a much quicker blockage rate from less media surface area, or worse sealing , worse anti drain, weaker bypass valve springs etc etc
and here bit of testing
again im not against longer intervals especially if long journey motorway trips etc(im worst really low annual millage lots of short trips under 10 miles) , I don't see the point of dropping oil and not changing filter.
its already partially blocked, not saying anywhere near unsafe but how many people would go for an oil change and filter and if the garage said ive got a used old filter here for free would say yes ill use that ?
its probably soaked in soot loaded oil(diesel) , which when you put your new oil in will contaminate all the new oil and continue to wear the internals with soot that passes through the filter as particles are smaller than media.
at your sort of milage ,editor id be thinking of maybe looking at oil sample tests for a few changes at extended drain each time as long as results still good.
have you ever done an 18,000 mile interval or have they always been less?
also to add I sometimes do a in between filter change as £5 is less than £40 and the oil top up helps refresh the oil for likes of tbn to keep acids at bay.
as said by others what your comfortable with, and can afford is what suits you, I don't think many on these sort of forums scaremonger, those that know some of the facts or details or have read seen or heard things about things pass them on.
there will always be a few that go against anything advised on forums for the sake of argument it seems.
read it all , investigate yourself and make a balanced choice.
heres a soot wear related item with a few facts and test results
bottom of this page has some visuals for filter manufacturers giving varying results, back to my first point of how long depends on filter and oil quality also.