OK, some interesting developments here.
Firstly though the washer part# is 877847, you need four. The valve guide oil seals are #436438 four of those too.
Interestingly though the 2015 models DO NOT use shims under the valve seats and the valve springs have a different #.
Early springs were # 874335 but they have a supercession to 82976R and in the parts list they are NOT listed for models with the early timing system as using a shim. BUT, there is no suggestion that these springs don't need the shims when rollerising.
What is more interesting though is that for 2015 models, already rollerised, there is another new part # for the springs. B013517 and these DO NOT use the under spring seat shims.
The part #'s for valves remain the same so extrapolating from this the new springs are slightly different and therefore DO NOT require the shims.
That being the case, rather than buying the shims, just buy the new springs and fit them in place of the early type?
I would still replace the valve guide oil seals, (You're in there, why wouldn't you?) but while the new springs will probably be slightly more expensive than the shims my first instinct would be to go with them rather than the washers which are by their very nature a compromise.