The "5 year life" is a myth - in the sense that there is no reliable evidence that valves fail after a specific period of time, least of all 5 years. Plain brass valves were the norm in continental Europe before the RCD and the only reason for including a minimum life was to indicate that seacocks are service items so should be inspected regularly. Although plain brass valves can dezincify this is relatively rare even after 10 or 15 years. The key thing is that the main body in not in contact with seawater and the only vulnerable areas are the barbs on the outlet spigot which can have saltwater resting on them and the threads in the through hull if the seal to the hull fails. Even if the spigot does dezincify it will only fail if it is stressed - indeed the test for integrity is to hit it with a hammer.
I believe 2015 boats are fitted with DZR - I queried this when I bought mine new that year and was assured they were. The main cause of failure on ball valves is seizure of the ball or corrosion of the spindle and handle. Regular operation of the valve reduces the chances of this. Marelon valves are not a direct replacement and doubt they would physically fit in the space. Also if the layout of the valves is like my 33 I think fitting Tru Design would be a challenge because of lack of space and the 90 degree bend on the outlet. Anyway other than operating all the valves regularly I don't worry about them at all. On my last boat, built in 2001 I replaced only the outlet at 8 years because it had seized and the spindle broke. No sign of dezincification on either the body or fittings.
