Dimmer not turn the LED on
IME the half-second delay is typical of many LED Dimmers. It's unlikely that a higher wattage will help, but a different brand might. You already have 150W (I'm hoping you are giving the LED wattage here) connected to 10W and 30W LED respectively. In fact, you may be running into an issue specific the LED dimmers, which is that many of them don't work well without a certain minimum wattage connected. I need at least 4 9W fixtures for the dimmers I currently have; on a switch, the LEDs turn on instantly, and on a dimmer they have that annoying delay. 

If a contractor, not you, did the job, the contractor should fix it. 

The "lowest dimming level" can be adjusted, normally, and should be so that all lamps are on. The highest is also normally adjustable. THose will be covered in the dimmer documentation, as will the issue of a minimum wattage, if that is applicable.