BGreen, nice choices, and it looks like you had a nice job on your hands there.
Taylor, since you want a bamboo under twenty feet, and you want a clumper that can stand 15 degree f, you definitely limit your options. Here are a few starting with the most expensive, and depending on whose opinion you get, the most beautiful. Bear in mind when I mention the lows for the plant, that means top leaf kill. A lot of the times, they can go a little lower before having its leaves killed off, and even lower before culm death. Even then, then root system can handle even lower, especially if its properly mulched, and if killed will send up new shoots in the spring. Another thing to mention is that the temp lows vary in a certain way. If a plants low is 25 degrees, then that temp often depends on how long its at that temp. For example, if 25 is what will give it leaf death, more than likely if that low is only for a few hours, then it will be ok. On the other hand, if its say at 28 degrees for eight hours, even though its known to go to 25, there is a good chance the tops will be killed. Other factors also play a role, incl. if it was watered before hand, and how well it was mulched, and if there is any wind protection. Wind as we all well know can be colder than the actual temp. Those factors need to be considered when dealing with plants in general. I would also like to mention that there is a nice little trick that can keep plants from dying, so long as its not a type that is highly prone to root rot from water. That is the use of a high volume mister when the temps are not extremely cold. The water coming out will be at a higher temp than the air around the plant, and can keep a plant from perishing. It can and does work, although certain factors can limit, or stop its effectiveness.
Bambusa chungii 'Barbelatta'
Max. height: around twenty feet
max. culm diameter: 1.50 inches
min. temp: 21 degree F.
Average price: about 80.00$ for a three gallon; might be able to get it a little cheaper.
This next pic is what it will look like mature, but just smaller. This pic is of B. chungii, which is exactly the same as the Barbelatta, but the chungii is the larger version.
The larger one is without a doubt one of my all time favorite bamboos.
More to come...