Bura Nut,
My experience with both is the 30x80 seem to have a better field of view but to me the clarity is the same. You have more options with the 15x56 though. The 30x80 are very heavy and I find unless the country is very thick you can cover alot more area with the 15x when glassing out to about 800yds. When I am glassing at 800+ I find my 30x pick up parts of deer better ie. bedded deer, deer behind trees etc. You can really pick aprt bushes with the 30x. Two experiences come to mind. One was when I was looking at an octillo thicket at about 300yds I saw a black dot in the middle it. I kept watching it and it blinked! With the 15x my friend could not see it. The other time we were glassing a valley from 250 to 800yds away and I was spotting deer looking through several trees. The 15x couldn't do it. I call my 30x80 my truck binos. I usually stay within a half mile or so of my truck with them because of the weight. The 15x56s can be used for all applications mentioned with two doublers. It only takes a minute to put them on or take them off. If you go on a walkabout the 15x56 w/doublers are far easier to pack especially if you bag a deer. Another concern might be money and the swarovskis are cheaper. If you lose anything I think it would be made up with the diversity of the 15x56 w/dbls. I also carry 10x56 with me and they have a tripod mt. too. If I want to cover alot of area quickly I can put them on a tripod. With the field of view they have you can cover alot of country. I have generalized a little and if you have more specific questions I would be happy to answer them. FYI, My friends call me the BinoMan. I have Zeiss,Leica,Swarovski, and Doctor binos. I have tried just about everything. For the money if I did it all over I would have 15x56 w/doublers, 10x42 swarovski, Leica 7x42 rangefinder, Leica 1200 rangefinder, 10x20 either Zeiss or Leica. One more thing to throw at you. I have 15x60 Zeiss and so far just one tripler. If you put another one on it you might really have something.
Rick