30A supply split to 2 15A arc fault, then recombined into 30A?
You're barking up the wrong tree.  Fix the sockets. Don't create arcing.
If you have sockets that are arcing while in normal use, then the plug or socket is defective and simply needs to be repaired.  You saw it happen, you know it happen, cash out your 401(K) and head to West Marine and get another socket or plug.
If it arced while you were plugging or unplugging it, well heck - that's normal when the boat is drawing a load when you yank out the plug or plug it in. You shouldn't do that.  Turn off the supply disconnect before messing with the plug, and then, you won't have that problem.  It would also suffice to turn off the boat-side disconnect (or all the breakers if it doesn't have a master disconnect/breaker).
Disconnect switches often look exactly like circuit breakers. They are simply breakers rated for switching duty.
Now, if you want AFCI protection inside the boat, you can feel free to get AFCI circuit breakers on all your 15A or 20A individual circuits.  If you have an obsolete or cheesy 120V distribution board in the boat that does not accommodate AFCI breakers, get one that does.  You may want to think about industrial-grade &quot;bolt-on&quot; (bolt-down) breaker panels and breakers. They're used in factories to keep unauthorized personnel from opening up panels and messing with breakers because the bolt-down bolts are hot... but they also work great when dealing with vibration or shock.
Mind you, AFCI breakers operate by &quot;listening&quot; to the power line and identifying that characteristic crinkle-crunch sound of a bad headphone jack or of connecting speakers with the power on.  They can't help hearing what's on the supply side of the breaker.  So even if the arcing is &quot;before&quot; the AFCI breaker, they will often trip anyway.  E.G. when you unplug the boat hot.
So... don't create arcing.
Why that won't work
As far as combining breakers... 30A is not made up of dual 15A.  OK, imagine you wire two 12V batteries nose to tail, and you call the middle neutral.  You then have +12V and -12V - use them both and you have 24V.  Now if you have a 24V, 30 amp load - is it drawing 15A from each battery?  No. It's drawing 30A from each battery.  Likewise a 240V/30A load.
Regardless, you're not allowed to combine 2 small breakers to substitute for a big one, so you can't use two 15's to get a 30.  Manufacturers will do that for very large breakers (gang four 100A to get a 200A/240V breaker), but they do it under controlled conditions and the whole assembly is tested and UL-Listed.
Even more than that, that doesn't work with AFCI breakers - because they monitor the neutral wire for current imbalance, both of the above cases will trip them.