I don't have that kit, but I'll answer the question based on general troubleshoot, and not specific mod dependent since it don't sound like a mod issue.
Having a very hard throat hit, can have many reason, the 2 most common are VG/PG rate and nicotine level.
You're using a max VG juice as you mentioned above, most manufacturer will list two numbers on their bottles/package or website. It will look something like this 70/30, 75/25, 80/20, 90/10 or even 100/0 that's very rare but I've seen a couple of these around. If nothing is stated on your bottle, I'll go by the majority of juices sold and marked as max VG available on the market and that's 70 VG/30 PG. I could explain that now in more detail but then we're here a bit longer, so let's just move on lol. Most harsh throat hits are from higher PG juices and unless you're very sensitive to PG, this won't be your issue or reason right now. But could always try a 80/20 later on, to rule that 100% out.
The other reason and what I do believe is your problem, is the nicotine it's elf. If you're sub ohming, most juices above 6 mg of nicotine can be very harsh, hell even 6 in most cases can be uncomfortable. Try a lower nicotine or get a mouth to lung tank/device that vapers at a higher ohm, allowing you to enjoy higher nicotine levels.
Grade of nicotine can cause the same, there's some companies out there, that sell low quality nicotine in their juices to keep cost down, at least in a lot of cases, that will when vaped create a harsh/burning throat hit. Some would call it peppery taste, I always compare it to cooking and using Tabasco. If you ever poured that over extreme hot stove tops or pan's, then you know what I am talking about. The vape created burns in your throat and even eyes, in some cases create discomfort. Its the same here, in that case switch the brand.
Some flavoring mostly fruits, when paired with shit ass nicotine can do the same, but in this case just steep or breath your juices for a bit and you should be fine, or again switch brands. Have to experience flavors/nicotine/pg/VG content/brands etc. It defiantly has nothing to do with your device itself at this point.