Fifteen ounces seems really small. Even the Camelbak Podium Ice-- which will keep ice for ~6 hours in 100º temps-- holds 21oz. And umm... "It prevents the beverage at 5 ° C -15 ° C temperature from heating at 20 ° C outdoor temperature for 3 hours." That's 68º.
In my summer riding (during which rides typically take place between 90-105º,) the regular Podium Big Chill bottles (25oz) will still have ice after ~3 hours.
The Polar bottles (not including the newer nanotech ones, with which I have no experience) don't stay cold nearly as long as the Camelbak.
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