If you haven't already look in the manual on the procedure to check your oil, then see if it does it and report back to us. Could be a sensor if the level checks out, maybe the filter??
As @Digdog mentioned, definitely check that and, similar to me, could be spark plugs. When was the last time you had them inspected or replaced? If it was recently replaced within the year, and the boat isn't run, it could go bad. I have the same engines as you, with a low oil pressure warning going off when starting up the engines. I didn't bother taking it off the trailer and driving around the lake and took it back to the dealer and replaced my spark plugs. You could replace spark plugs yourself, i've personally done it, but I took mine to the dealer because of other reasons that I had from after picking up from repairs.
If you have the right tools, which is really just a spark plug socket and inexpensive, and takes 5min to check a spark plug.