I wouldn't mind seeing Lang re-signed but no way at that deal. 4 years is too long and $15 mil is too much risk. If in two years he's fully broken down that's $8-10 mil dead cap to eat. The Packers aren't going to structure that one.
Halve that deal in every way and that's more realistic. Or if there's a 3rd year it's not costly to get out from under.
Lang is a hell of a player. Tough, experienced, everything you want in the trenches - except old and beat up.