If I lower the tongue weight to the recommended 150 lbs does anybody think it will help my sway problem ?
Do not do this. It can kill you. Sway is often the result of too little tongue weight. More is usually better but too much and you can start bouncing the front axle off the road. You need to figure out what the weight distribution is before you start experimenting.
You're missing an important piece of information - the total rig weight. Any figures in the manual are probably way off by the time you add gear, fuel, water, and hang an engine off the transom so you need to drag it into a truck scale and find out what the weight is on the trailer axles.
Total weight = tongue weight + axle weight.
%tongue weight = tongue weight / total weight.
Most bumper pull boat trailer manufacturers recommend between 5 to 10 percent tongue weight, occasionally 10 to 15 percent. 10% usually makes for a stable tow.
As Redfin says, while you're at it look for loose parts, misaligned axles, or other mechanical problems. I'd bet though that you have a light tongued rig that is responding differently to a change in suspension geometry with the new van.