It is most likely an intolerance. I had the exact same thing happen when I started drinking protein shakes. I bought the cheaper stuff at Walmart, and though I liked the flavor, it made me very nauseous, and thus I started to shop around. I thought it was an overabundance of whey, but then I got a different brand I couldn’t find in stores that was 100% whey off Amazon, and the nausea stopped. Thus I link it to the sugar content or the soy that was in the other brand. Speaking of soy, that can do that to you (make you nauseous if you not used to consuming soy). I love honey roasted soy nuts, but too much really can make me sick. I am not sure why (haven’t researched), but my opinionated assertion is the link between the hormones soy contains an my own system (isoflavones that mimic natural human estrogen), but this is speculation. With Soylent, I have surprisingly NOT had nausea with it, and honestly did not think of this potential when I first got it (it’s been years since I’ve had roasted soy nuts). With the protein shakes, even though both products I have tried have soy in them, one works with me and the other doesn’t. Soy is a strange thing, and it’s combination with other ingredients can make it a hit or miss on ones body if its not to the body’s liking. Worst case scenario, your body cannot handle Soylent. At best case, you can slowly allow it to adapt to the new food. In either case, there will be better soy related products that will agree with your system more, unless you have a straight up allergy of it (of which you would know because many food products contain soy and you would react the same way to all those products to different degrees).
My best recommendation is to eat crackers or bread, something that will “soak up” the drink in your stomach, making it less likely for nausea to occur. Drinking it slowly won’t do you any good if it happens more than 10 minutes after the fact. Malnourishment symptoms will continue, and not ease after a 30 minutes or a day if that’s the case (actually if you are malnourished, you more likely to get sick and stay sick after eating anything, not just Soylent). Diluting it further may help (drinking more water), but that will only get you so far since your body still has to process the ingredients. Again, I would say to not consume the Soylent alone, and slowly wean yourself off of supplemental foods if you want to go 100%. I would say take a month to do this. I don’t know if you have pets, but when you switch them to a new staple food, you can’t go “cold turkey” on them, or else they will get sick and puke. You have to slowly introduce the new food by increasing the new food and decreasing the old food over a period of 2 weeks to a month depending on how the pet handles it. Do the same thing with Soylent. But take it at your own pace, if you start to feel sick again as you wean off, maybe your body just cannot handle Soylent alone. Back to the pet analogy, I got a new food for my cats and hedgehog (they ate the same food, and the kind we were getting them skyrocketed in price in a short time), my cats took to it very fast without problems, but my hedgehog got very sick after only one night (I had only 5 pellets of the new food for him just to try among his full bowl of old food), and immediately stopped trying. I now get smaller bags of the old food because it goes farther for my hedgehog, and new food for my cats (for those interested, I went from Blue Buffalo to Taste of the Wild). Again, just listen to your body, it knows you better than you do.
Hope this helps.
Edit: I drink the 1.5. It does have soy, but since I have not tried the 2.0, so I am not familiar with the differences between the powder and premade drink (I don’t have the fridge space, I use individual scoops in blender bottles for every meal, and put water in when I’m ready to consume it).