How long the demo software is valid for?
The MATLAB R2015a is not delivered as a DEMO application instead its licence is TRIAL which means you will have 30 days to test the software after which it will stop working and you'll have to purchase and activate it if you want to use it again on your PC.
You can find more information about the product using the following link: http://www.mathworks.com/products/new_products/release2015a.html
