Hey mate,
The 150W will surely be enough for 2 plants. If you want to fill up your growspace then you have to get an additional light.
Good luck and happy trails for the rest of the way 🤞
Servus
OimRausch
Unfortunately, you will need a bigger light for a 4x4 tent. If getting a bigger light isn’t an option I recommend only growing your plants to take up a 3x3 space in a 4x4 tent. Hope this helps, good luck.