the 15 is effectively a 24 replacement (far fewer of those about) my 14 i bought specifically because it replaced the 21 fov for me. it's been one of my most used lenses
Like the idea of the 21 (a good 28 replacement i guess since there is no 18) but it's too slow IMO it should be 2.0-2.4 but then it would be bigger
you are right you can't crop wider
a good decent side is very useful (spend some time in small European streets and it's apparent pretty fast, I've often wished for even wider than the 14 when on vacation. it's the one lens guaranteed to be in my vacation kit. The second is actually the DA35 2.4. ideally i would have a 70-77 to compliment those 2 - in fact the 4 da 15-21-40-70 would be pretty ideal)