Can you power a LED with a lower tension but the right current
First, anything that operates at 30 V and 1.5 A is not just a LED.

Since we can only guess what your device really is, there is no way to say for sure what it will do if you try to give it less voltage or less current than the spec.  Probably it will just get dimmer until at some point it emits no meaningful light at all.  That could be at well above 0 V.

The obvious answer is to just try it.