Having the 1500 lbs tongue weight limit on the hitch rating might not be enough....it will be close more than likely. As you already know, adding toys in the rear will definitely reduce your tongue weight, especially if you are carrying TWO bikes of the size/weight that you have. Your payload capacity is almost identical to the F250 that I had (2148 lbs) and with a trailer tongue weight starting out at approx. 1400 lbs, (the new 2018 model you mentioned) before loading the bikes in the back, the tongue weight will be less than that amount. Herein lies the problem with Toy Haulers.......more weight in the back reduces tongue weight. Reduced tongue weight vs. Gross Trailer weight = not enough tongue weight and trailer sway. Trust me, I've been there, done that, and experienced the lighter tongue weight and trailer sway. When that happens, the only option is to add more tongue weight to get it up to at least 11.5-12% of the trailer GVWR. 12% on a 12K GVWR trailer is going to be 1440 lbs of tongue weight. Depending on how much weight the bikes remove from the tongue weight, you might be trying to add at least a couple hundred pounds to the tongue. In my case, which is almost identical to yours weight-wise, here is my progression on adding weight.
1st attempt: removed single battery and box and added two 6volt batteries and box plus a 35lb barbell weight up front under the baggage slide. That added approx. 125 lbs to the tongue weight. Still not enough tongue weight and still had sway issues. Everything was weighed at a CAT scale for the numbers....no guessing....slightly over 10% tongue weight.
2nd attempt: Added water to the fresh water tank to completely fill it....106 gallons. Because of the water tank location, that added approx. another 120 lbs of weight on the tongue. Still had some sway issues, although not as bad.....but still noticeable. NOW, based on the CAT scale weights, my F250 with a GVWR of 10,000 lbs is almost at it's max. Part of the reason for this, and a big part, is that I have a 42 gallon aux. fuel tank in the bed of the truck which adds about 310 lbs, plus the tank and pump....another 125 lbs for a total of just under 450 lbs. Of course this extra weight increases the total weight of the truck, and significantly reduced my payload capacity to the point that I didn't have any more "room" to keep adding weight to the tongue of the trailer without going over the truck GVWR......and that's with the trailer loaded exactly like it is when we travel with it.....bike, pit bike, tool chest, pop up canopy, fuel in the 30 gallon onboard tank.....everything. So you can see that loading the rear of the trailer with lots of "stuff" will definitely affect the tongue weight of the trailer.....to the point that you may not have enough tongue weight and will have to add more to get to the 11.5-12% of the trailer GVWR.
In summary, it's going to be close for you on your weights....very close. Your situation is almost identical to mine and I made the decision to buy a 1Ton truck to be able to handle the trailer comfortably. A SWR would have more than worked for me, but I chose to buy a Dually (F350 Diesel) to have more than plenty of room for future upgrades if I desire to do that at some point.
Oh, I forgot to add the third attempt: Once I traded trucks and got one that could more than handle adding weight to the front or tongue of the trailer, I added two 60 lb sand tubes to the front baggage area, which because of the close proximity to the front of the trailer, most of that weight was added to the tongue weight total. I now have 11.5% of the trailer weight (12,500 lbs) as tongue weight and the trailer doesn't sway anymore. Dually stability, enough tongue weight, and no more white knuckle driving!