On all the scales I've seen, 1.15 pounds means 1 pound and 15/100ths of a pound. There's 16 ounces in a pound. So .15 lb x 16 oz (per lb) = 2.4 oz. So I think this pup is 1 lb 2.4 oz. or 18.4 ounces.
Other Examples:
1.5 lbs = 1 lb 8 oz = 24 oz
1.75 lbs = 1 lb 12 oz = 28 oz
2 lbs = 32 oz
2.5 lbs = 2lbs 8 oz = 40 oz
I'm not sure how your scale reads (does show pounds and ounces, or just show pounds?), but this is how the scales at my vet's office work.....
Does your scale ever read anything higher than (for example) 1.16 lbs? If the .16 were ounces, then the scale should really show that the dog is 2 lbs (since there are 16 ounces in a pound).... (1.16 lbs = 1 lb 2.56 oz = 18.56 oz)
Here's a nice little conversion chart:
http://www.aqua-calc.com/wc_pound2ounce.php
Piper: My cousins have a small Chi (he's probably 3 lbs max) and a 25 lb Cocker mix. They all get along great. I think as long as the larger dog is introdued to the smaller while it's still a puppy, they'll get along fine (as long as the smaller dog like the larger dog too!!)