Your shelves should be adjustable, IMO, and spaced to suit items you will place on the shelves. Uneven spacing does not look random--it looks "real", like you live there instead of in a staged showroom. If you prefer an orderly look, line up some of the shelves on each side of the fireplace but include some that do not line up to avoid that too perfect look.

I saw something like this just the other day that was beautiful. They had added just one more shelf up top creating a larger space in the center of the bookcase. They used the larger opening for a pair of small table lamps and a few books on either side of the lamps. It looked great on either side of the fireplace and created a wonderful ambiance in the room at night. They also finished out the top of the bookcases with substantial crown molding and it looks like pieces of furniture and not bland bookcases.

Adjustable shelves. Ha. This is a DIY project. But thanks anyway....

I agree with Shellril or make the top shelf larger for decorative items and the inbetween smaller.

yes, do adjustable with the tracks shown, thats what we have in our back hall and i move them around frequently.

if you don't wish to do adjustable, at least do removable shelves, so that you can get a larger area where you like, flexibly.

Just do them every 12 inches. 15 is too large for upper shelves. Make sure it will work out -- you could shave to 10 if needed near the top.