2015-P Roosevelt Dime - Interesting Die Deterioration.or Not ?

Well it would be common. It was mentioned once that 54% of the coins come from VLDS die state dies.

So it is common. It was not like this was the last coin struck by this die, but one of many coins struck by a worn out die.

Why?

I don't know for sure, but perhaps most dies are retired before their maximum possible lifespan is up? That estimate was for dies that are used as long as possible.

Now I am wondering if this is a die trial strike, or die adjustment strike, where the striking pressure was not properly set. That seems to be a logical conclusion since both sides are equally affected. The convex shape of the die at striking would lead to the centers striking up better as exhibited and the outer areas near the rim less so. Any new thoughts on this line of thinking? The following image is credited to the NGC educational error area of their website. They also note that these type of strikes rarely escape the mint.

What you're seeing is textbook die wear, not strike weakness. Die Deterioration is characterized by distorted devices and flow lines in the fields, as seen on your coin. Weak strikes are just unstuck at the high points (around the edge, middle of the portrait).