I don't do tri's, but as you can tell from my avitar, I spend a lot of time in the water. 68 is cold. The biggest problem you will have is the cold zapping all your strength. You will be much happier if you keep your core warm. You will lose too much energy (even though you will feel warm because of the exercise). I spend hours at a time in the water, and believe me, even in 80+ water, I wear a wetsuit to keep my energy up.

They have neoprene vests and suits with zippers. If you don't want to mess with peeling off the legs, look for a "shortie" or a vest. Consider a hood to keep your head warm--it's where you lose the most heat from your body. Check out some scuba websites for wetsuits, you might see something you like better.

Just my .02 cents!