1)Combination waste and vent has a vent pipe which runs horizontal for 15ft and than rise up through roof. UPC does not have any paragraphs to object this. Does anybody know what the risks are. THis is a system serving to one floor sink only with 2" tail pipe and 3" waste line.

Sounds like a paragraph on 'dry vent' would cover this. You must rise at least on a 45 degree angle at least 6 inches above the flood level rim of the fixture before changing to a horizontal flow.
I personally think it should work though

Thanks Doug. I think it will work too.

1)Combination waste and vent has a vent pipe which runs horizontal for 15ft and than rise up thru roof. UPC does not have any paragraphs to object this. Does anybody know what the risks are. THis is a system serving to one floor sink only with 2" tail pipe and 3" waste line.

Is the horizontal portion of the vent below the flood rim of the floor sink?

If it is, the UPC allows you to flat vent below the flood rim if you use drainage fittings (long sweeps in horizontal to vertical transitions) and grade it 1/4 of an inch per foot to the drain.

The flip side, of course, is that an inspector will look askance at the rough-in if there were other ways of plumbing it that avoided flat venting the fixture.