If you're dropping the pan, change the filter while you're at it. You have to get a new gasket anyway, and the filter kits take care of that. If you drop the pan on a good schedule, you shouldn't need to flush it.
With that said, tranny flushes are not "risky" - on a properly maintained transmission that is flushed/changed regularly. Now, that doesn't mean it is necessary to flush it every 15k, that's overkill. Of course, a flush can be a very bad plan on an old transmission that didn't even have the pan dropped in 150k. The flush itself might not be the true culprit, but it could end it in one shot. In that case, you would be better off just draining and replacing a little fluid or doing nothing, at that point.