The Sigelei 150w is more than sufficient.
With regulated devices you don't have to go super subohm to produce clouds. Sometimes, having a wider, more resistant coil can produce more vapor. This is due to the surface area of the coil. More wick being heated, more vapor. All that needs to be done is add more watts.
With a mech you're limited to your build and battery. A smaller, less resistant coil will produce a lot of vapor, but thats about as good as it gets.