GTC
The company can want all they like, but when the housing increase to 25 years was put forward last year aloing with the SLS package, I distinctly remember no pre conditions or trade-off's. It was simple improvement for BOTH parties and could have been signed off in 2 minutes if the will was genuinely there.
As far as I'm concerned, keep it at 15 years and be done with it. All this crap is happily spread by management or management wannabe's(the 'in the know' types who just love being that) and ends up being of huge benefit to management in the form of expectation management and ad-hoc negotiations.