YZ 250 : 2005 plastics on a 2015+

Should be as you only have to change the airbox to go from 2005-2015. Front plate mount may be different? But I think it is the same too.

Airbox is needed for the older sidepanels to fit and from what I remember, the front fender/plate mounts different. When I had an '05 125, I wanted the '06 front plate and fender when the 06s came out. I remember having to drill different holes in the fender and getting creative to get the plate to mount (I had to use a thick spacer for the front bolt etc.) So I'm not totally sure how that would be, going in reverse.

Like AH387,  I also have an '05 125.  I kept the old style look, but learned a bit out the differences between years while upgrading to 2012 SSS forks and triple clamps.

On the 125, which uses mostly identical plastics to the 250 (part numbers match), the only major change from 2005 to 2017 is the front forks went from AOSS to SSS in 2006 along with a different triple clamp, with the forks mounted 2mm further apart, and I believe in 2006 is when the number plate mounted differently.  To be complete, the engine got some minor changes in 2006 as well. Head shape, power valve spring that keeps the power valve open another 500RPM, and ECU changes to match.  The carburetor changed as well.

The fork guards are not interchangeable between 2005 and 2015.  That changed approximately 2008 when the brakes (and fork lugs to match) changed to a smaller distance between mounting bolts.  It's going to be easier to keep your 2015 fork guards.

When I upgraded my '05 125 to SSS forks, I found out what changed year by year by comparing the part numbers in the OEM catalogs.

My understanding is that the frame is effectively identical from 2005 all the way to current, so what you want should be very doable.