2 team 15's on 2 5k's is gonna rip any trunk apart haha.
the biggest benefit of going sealed is a more stable/flatter frequency response and better transient repose curve(what most relate to a cleaner/tighter bass). Thats not to say that acceptable levels of either aren't attainable ported.
Your 2 systems you're considering are drastically different. I feel like fitting 3 15's in a trunk would be pretty tough. you'd probably have to fire them up and your trunk lid would hate you for it.
Teams would surely be louder. I cant comment on how they'd sound as i've never heard one.
With something like that where the bass will be pretty trapped in the trunk maybe a 4th order with 2 15's ported through the rear deck? Not sure if you've got the room for it or how the rear deck is constructed but its an idea.