You have 30 days (starting from when Dell shipped it out) to return the monitor. After that, I believe it is a 3 year warranty. Since you just received the panel, call customer service and tell them you want to replace it with a NEW one because of all the dead pixels. After your 30 days has passed, you have to go through tech support which will send you a refurbished panel.
Every panel will have a few, but 15+ is too excessive.
Call tech support & get the monitor Exchanged for a NEW one
Inspiron E1505 Windows 10 / XPS 10 Windows RT
Dimension 8400 Windows 7/8