The one clear advantage of the BCT15 over the 898 is alpha tagging. I use a BC890xlt (very similar to the 898, but without trunking) for listening to all the local conventional fire tone-out channels and aircraft frequencies, as well as for doing quick manual searches. I love it for that purpose. It is much easier to control on the fly than the BCT15, and the big tuning knob is very handy for searches. But I do find myself having to look at my frequency list a few times a day to figure out what agency I am hearing at the time. Of course, that's not such a concern in a more rural area where you aren't surrounded by so many agencies.
If you want something that is easily programmable on the fly for immediate frequency entry and impromptu searches, I'd recommend the 898. But if you want something to just program and forget about, not needing much direct channel entry, and cannot live without alpha tags, then go with the 15. There's only about ten bucks difference between the two either way.