I had picked up my boat after a very lengthy and extensive repair. I too had a low oil pressure warning for one of my engines. I didn't actually take my boat of the trailer and drive around and instead took it back to the dealership. They ended up replacing my spark plugs as, if the engine is unable to run smoothly, it will be unable to maintain proper oil pressure as the RPM rises. I have twin 215 engines so it was obvious for me to see and hear the difference between an engine with and without low oil pressure. At idle, sounded a bit rough and like a lawn mower, with some visual shaking when looking from the helm seat at idle. My other engine that was fine sounded more jet like with higher RPMs to the point that it wasn't very visible to see the engine shaking.
When was the last time you had your spark plugs changed? I usually change mine every year and really don't cost much to do that. I had mine replaced last year, but it spent 11 months being repaired and only driven a few hours at the dealership for testing that mine went bad when I picked it up.