Well you can capture long reverb halls/stadiums all day long. up to 15 secs or more if you want. - But by the time you deconvolve them into an IR.. no processor will run them. (you can run them on your Computer ofc) but only 1.. and that is even painfully sluggish.
You may then say.. AH yes.. but there are tons of plugins out there that do reverb for longer.. Yes.. see its clever trickery.. often they will use a VERY Small IR (maybe the first second, just to get the base tone/spectrum) then the rest is done in code realtime.. : )
an yes Im 100% confident the kemper cant do it due to processor power.There is not a single unit out there that can
3 secs is still not enough to capture the heart & soul of Amb/room mics in a good room. on our tests we did the best results were about 6 secs or more. this was a very true lifelike "static" snap of the room.