Yes, most shrining programs are designed to make the disc fit onto a single layer disc.
Even though DL discs hold "4 hours" of video on them, you'll find many with 5 or more hours on there. It's all about compression.
Use DVD shrink and enable all the settings for the best quality compression. You'll find that even a 3 hour movie won't look much different to the original unless you have a massive TV.