I lose picture and sound on my Viore TV after 15-20 minutes although the light is still green. I have to turn tv off for about 10-15 minutes and then turn it on to get the picture back?

Chances are this is a main board issue however it's never good to "throw boards" at a set, take the back off and power it on tell it shuts off, test the various power supply voltages, if they're good replace the main, if they're incorrect replace the power board, I think you will find this is a main board issue although it could be either.

This issue with losing picture and sound on your Viore TV after a certain amount of time can be caused by several things:
Overheating: If the TV is overheating, it may cause the TV to shut off to prevent further damage. This is usually caused by poor ventilation or dust buildup in the TV. Clean the dust out of the TV and ensure that it has proper ventilation.
Power supply issues: If the power supply is not functioning correctly, it can cause the TV to turn off and then back on. You can try checking the voltage readings at the power supply to determine if this is the issue.
Bad capacitors: Capacitors can go bad over time and cause the TV to shut off and then back on. You can check the capacitors on the TV's power supply board for any signs of swelling, leaking, or rust.
Main board issues: The main board of the TV could be malfunctioning, causing the TV to shut off and then back on. If this is the case, you may need to replace the main board.
If you're not comfortable with the above steps, it's best to contact a qualified repair technician for assistance.