Just put in a 2 1/2 ton today, and it does list the 15 kw on the nameplate as an accessory. The element sits at the edge of the blower outlet when installed, I looked in through the hole I cut for the humidifier being surious after reading this thread.
The heater access I mentioning was referring more to other brands than tranes. Didn't think of the few conponents behind the breaker, but its a lot easier to pop the breakers off a trane heater than others.
I had to check the relays on some generac brand that put ALL the relays,wiring,limits,etc behind the plate the breakers were in (dc relays by the way) so had to pull WHOLE heater unit. The screws holding the breaker plate faced into the cabinent, unlike Trane's that face out so you can get to them.
Gibson has the same type heater as the generac one one took apart, but they have the top of cabinent so you can take it off and access stuff behind the breakers.