Not at all. Both types of gun will gain velocity as the barrel gets longer until you reach the point it is too long and powder is consumed, then the bullet will slow down. But neither gun needs a barrel so long it is 100% efficient.
If you have a 15" TC and a 12" S&W, the difference is so little you will never tell in the field. To tell the truth I would go with a 12" TC, larger is a rifle without a butt stock.
I have to look at the S&W because I believe it has a gain twist so if you shorten too much you will lose spin. You can go to 6" and still kill game but your range will be shortened. Accuracy might get worse because of twist rate. This is not true with the TC.
You can get higher velocity from the TC only with seating depth, bullet choice, barrel length, etc. Loss from the gap of the revolver should not turn you away, it is not huge. A TC compared to the revolver with the same barrel length and load will both do the job.
Take both guns with a good scope and shoot 200 yards. Drop between them should be no concern, after all, a click or two on the scope will put you on target and you might not need it.
If you think higher velocity will kill better, you might be mistaken because it is bullet work that kills, not how fast it goes but how they work at the velocity you shoot them.