My vote is for the 10. No sight adjustment needed.
Assuming, of course, that the Model 10 "sights" are properly regulated from the factory in terms of poa to poi. Because if they're not (and I've had more than a couple of handguns with fixed sights from great companies that weren't) your choices are limited in terms of a fix. If the gun is shooting high (and I have a Colt Cobra that shoots at least a foot high @ 25 yards), you'll either have to add metal to the front sight; change it for a higher one (assuming it sits in a dovetail or is "pinned" on) or try different bullet weights and hope the poi changes significantly enough to conform to the poa.
It's a little easier if a gun with fixed sights is shooting low. Judicious use of a file on the front sight generally will cure the problem.
Windage adjustment on a gun with fixed sights poses the biggest problem. If possible, a careful bending of the front sight might bring the sights in conformance with the poa. Otherwise, a trip to the gunsmith is probably in order to torque the barrel from a vise in one direction or the other-and this will be trial and error at best. Changing bullet weights will usually have little affect on windage corrections.
As a last resort, I suppose a shooter could employ "Kentucky Windage" when making a shot. Good luck on that option if you have to use the method on different guns and to remember which gun to "hold off" on and which one to "hold on" to.
I prefer adjustable sights on most of my handguns. I often shoot different cartridge/bullet configurations and combinations, sometimes at different distances, that generally changes the poi and I like being able to change the sights with a screwdriver to bring the sights in tune with where the bullets are printing.
Adjustable sights are almost always easier to see in terms of aiming and getting a good sight picture than are fixed sights.
I think way too much has been made over the supposed fragility of adjustables. I carried a revolver having adjustable sights for much of my thirty year le career and only once, during a roll on the ground resisting arrest scuffle, did an adjustable sight on my revolver ever break. And that break was to the "ear" of the blade and would have made no difference in any event if I had to use the gun at that point-blank range.
Handguns with fixed sights certainly have a place in any ccw role where the gun has to be drawn from "deep cover" or even from a pocket; areas where an adjustable sight might snag during the draw when time is of the essence in terms of surviving an armed confrontation.
So for me at least, the choice is a "no-brainer": the Model 15, especially if the prices of the two revolvers are close to being the same. And for those that don't like the original grips on this K-frame variant, it's easy enough to get an after-market set that are better to your liking.