well, the B-15 is a legendary bass combo but is a fairly limited, almost one trick pony kind of thing. At 65 watts (or less, I think) it does not have much overall volume despite it's great tone. It's also a bit of a beast for transport, heavy and on the bulky side, and maybe a bit delicate for the pounding that your gear will typically take during steady gigging. So, for $2k, I think there are a number of better options.
Disclosure: I am a Walkabout bigot for sure, so take my comments with a grain of salt.
The Mesa offers what many here consider a modern and improved B-15 approach. Lots of tone options between the tone controls and the para eq, from clean and articulate, to tube warmth, to crunchy and distorted. Plenty of volume for just about any gig (300w@4 ohms, 500w@2ohms), nice DI, very flexible - you can take the head out of the combo to drive other cab(s) combinations, and it will run stable at 8, 4 and 2 ohms (as discussed on TB repeatedly). Also this combo is extremely portable, particularly with the Mesa roller attachment thing.
It comes with a 5 year transferable warranty, and Mesa service is pretty renown in the biz.
So anyway, just my 2cents, but for the kind of money your talking for a playable B-15, I'd go with the Mesa.
New, you can get the Walkabout 12 for $1199, and the 15 for $1299. They come up used fairly often here and on the other used gear sites for between ~$750 and ~$900.
Good Luck