I don't even use my 2" chisel any more. I use my 1-1/2" on 1.5 and 2" mortices, and only on the ends and after the 3/4" corner chisel. Every thing else is done with a slick and it has nice slender sides to it. Lousy knots are an exception. If you were hand boring one hole in a mortice and chiseling to the hole then a good thick stout chisel would be desirable, I suspect. On tenon work I don't even pick up a chisel, it is all axe and slick, no mallet and chisel chunking. And I don't mess with hand planes on tenon work either.

So my opinion would be to get a 1-1/2" beveled edged chisel for the purpose you mentioned, it can get into tight corners when cleaning up the ends of the mortice.

Hand planes.... I love my scrub plane, it serves as a thickness planer for when thing are too fat.