ive never tried a guitar amp with a 15" that ive liked. for example, side by side comparison of a twin ri with two 12's and one with the 15" i much prefered the 12's. some people love em, some dont.
why not a classic 50? it should work just as well as anything.
the delta blues is the peavy that you are thinking about that has a 15". the amp is pretty similar to a classic 30. ive tried both the two 10" and 15" versions of the delta blues and i like the 10's better.
I have an Electro Voice SRO15 sitting in my closet... never heard it.
I have an EV 18 in an old Musicman cab. Opened up the back, and that mofo has AMAZING, beautiful tone. Big open roar. I generally use it with my 68 Bassman, but my Traynors kill with it too. I love the sound of 15s but don't have anything recorded with it, but there are a lot of similarities with the 18.
Here is the Bassman, EV in action.
http://www.soundclick.com/util/getplayer.m3u?id=5664483&q=hi