There are lots of 15 gal kettles that work. Biggest decision is Al vs. SS. People get good results with both. Just be aware that that with an Al pot you should passivate the surface by boiling water in it for a while (check in the forums for details). There are also some types of cleaners that should be avoided with Al (again check the forums.) Spike Brewing has a good
pro vs. con for Al/SS. For SS pots, Concords and Bayou Classics are popular and fairly inexpensive.
Ball valves are handy, especially if you have more than about 6 gal post-boil. I don't have any problem lifting my pot to an elevated surface and using an autosiphon to fill the fermenter @ 6 gal. More than that, and I would have to have a valve. If you're handy with DIY, installing your own ball valve is a straight forward project, either weldless or soldered (use the special solder fitting from
BobbyM if you want soldered.) If you want welded,
Spike Brewing has reasonable prices on pots with standard or custom welded fittings.
Skip the built in dial thermometer, they can get in the way when doing BIAB, aren't the most accurate, and can't be moved around to check temp in different locations. They seem to be most useful on HLT's in 3 vessel systems.
Go with an immersion chiller. Plate chillers have a big cool factor, but they can clog easily and are difficult to clean (and impossible to inspect.) There are other styles of counter flow chillers that are less clog prone. You also really need a pump when using a plate chiller.
These are my opinions, others may disagree.
Brew on