It’s a 15 year old roof with an architectural type shingle. The built up areas are not another layer of shingle it’s just more granules on the shingle.
The question is, the built up areas only have cracks, is this a concern? It didn’t look like the cracks went below the depth of the top layer, but it’s hard to tell.
A picture of the ridge cap shows how the built up are is cracked but not the original layer.