Macbook Pro screen display problems
Since you have a 2015 MacBook Pro that uses Integrated Graphics (the Intel Iris Pro chipset), you can be assured that what is manifested on one screen, will manifest on all.

What this means is that the lines you are seeing on the screen are not due to failing GPU but rather the LCD itself.  You confirmed this by plugging your MBP into an alternate display device (projector).  

If you have this under Apple Care, you should take it in to have it repaired straight away.  To fix this, you will need to replace the entire Display Assembly and unfortunately, they are very expensive (approx. $850USD).