Valves are the same between the 2015 R8 V10 and the RS5 with one minor difference...the stem diameter is a few hundredths difference (just use the proper valve guide).

Intake Valves
Intake valve face diameter=33.85mm
Intake valve length=103.97
Valve seat ange=45 degrees

Stem diameter RS5=5.95mm
Stem diameter R8=5.965

Exhaust valves
Exhaust valve face diamter=28mm
Exhaust valve length=101.9
Valve seat angle=45 degrees

Stem Diameter RS5=5.96mm
Stem Diameter R8=5.955

So there may be some benefit going to the 2nd get (2016+) exhaust valves if they are indeed one mm thinner in stem diameter. The third gen (2019+) uses titanium exhaust valves if I remember correctly.

One place you may be able to check is someone like Underground Racing. They may be going with aftermarket valves, springs, retainers and other bits. Not all of that will be useful as they're building super high hp forced induction engines. If you do not go with cams, there's probably no need to go with aftermarket springs. I could see going with titanium retainers for weight but that'd be making such a small difference. But...if it's an off the shelf item, already in existence, you're probably looking at $500 for all 32 valves. Personally, if you're not racing the car, I'd stick with as much OEM in the valve train as possible for reliability. JHM has been running their RS5 to 9,000 rpm and hasn't broken anything yet.