I think you have a very unique configuration. You are leading the charge up this hill, and you may not find anyone who has crested that hill here to give you any advice as to what exactly will happen when you do crest that hill .
Here's the problem:
1. When you load up a tripod with more weight, without changing other variables, it performs more poorly.
2. When you increase focal length, even without adding weight, the tripod will perform more poorly and more or less in direct proportion to focal length. This is why Gitzo has developed their chart of focal length verses series.
3. For the most part, as focal length increases, so does weight. The exception is something like a 300/4 verses a 300/2.8, or a something-500 Sigma f/6.3 zoom verses a 500/4.
What you do not often find is significant weight coupled with modest focal length, as you have here, with a 15 lb payload at 200mm or less. Your payload is typically only seen with a 600 f/4, and I can say with virtual certainty that a Series 2 cannot handle that for your application (landscape).
You do have an advantage that, for the weight, the 70-200 is rather compact, where something like a 600/4 has a huge moment arm factor and side profile that adversely affects things, especially in the slightest breeze. A 600/4 acts like a huge lever where the 70-200 acts like a somewhat more modest lever, but still much more lever than a small prime, for example.
You have another complicating problem in that most long focal length work is not done at slow shutter speeds, and we often get into debates that actually touch on this point. Most people don't shoot sports at very slow shutter speeds that require more critical precision, and the same is generally true with birding.
The only common usage for long focal length at slow shutter speeds that I an think of is lunar imaging, but even there the moon is moving and that puts a floor on the shutter speed. You have no enforced floor.
I would assume that your landscape work might need to be done at almost any conceivable shutter speed- that is the nature of landscape work. But where landscape is typically done at under 100mm you presumably will be using longer focal lengths, up to 200mm, in order to extract maximum detail, and then you will simulate shorter focal lengths by stitching. That's what Pano is all about!
1. You may find it difficult or impossible to find anyone that has done what you are trying to do, in terms of weight vs focal length. And...
2. Depending on what exactly you shoot, and the shutter speeds, you could easily push 200mm to an extreme that would not be a huge problem with a 7lb payload but could be a huge problem at 15lbs.
My recommendation is that you try it with your series 2. If I had to lay odds up front I would put money on your having problems. But I am making a number of assumptions and extrapolations so I could be very wrong.
I would recommend that you have a fall-back position and be prepared to acquire a much beefier tripod, and I'm not sure the 3022 Berlebach is the right answer because, as previously mentioned, the payload ratings are the same. That in itself - wood vs CF with this unusual payload combination, would make for great research in the interests of science
I would have no concerns at all for the safety of your gear- a Series 2 is designed to safely support it. So you have nothing to lose as long as you are committed to using the Gigapan, one way or the other. And you will learn things with the Series 2 that no one can predict unless they've done the same or very similar with that 8lb panning base.
I would, at a minimum, use a Markins TB-21 replacement top. If there is any application where the TB-21 will help, it is here, and I suspect hte relative benefits of the more geometrically stable Markins top will prevail in ways we do not normally see, Among other things the Gigapan will make the whole thing very top-heavy, similar to a gimbal but probably much worse.
One point of research is the attachment thread. Their literature says "can be connected to any tripod" but then specifies a 1/4" thread. I can't believe they built that monstrosity with a 1/4" thread, verses standard 3/8" thread. That might present some challenges with a TB-21. They apparently figure you will mount it on top of a standard head on the camera platform, and the 1/4" thread may actually force you to do that, whether you like it or not.