A software company is adopting Lean principles in its software development lifecycle. Calculate the Defect Density for a recent software release that had 15 major defects and 500,000 lines of code. Suggest strategies to decrease Defect Density and explain how reducing Defect Density aligns with Lean principles in software development.

Requirements:

1. Calculate the Defect Density.
2. Suggest strategies to decrease Defect Density.
3. Explain how reducing Defect Density aligns with Lean principles in software development.