The conditions of waivers are that 1. it is not principal private residence, 2. you cannot get life cover at all, 3. you can only get it at increased cost or 4. you are both over 50.
This is not exact wording but close enough, none of these apply to you and banks are so procedure led that maybe they don't consider a waiver will apply in your case. What if you apply for full cover for the full term and then obviously you will get a refusal and then can you slot in No. 2.
This is quite common, lots of illnesses cause these difficulties, even diabetes can cause someone not to be able to get life cover. Banks don't have to accept waivers, each has their own policy on it, check a few until you find one that does. You can then still take out the 15 yr policy to cover yourself but it will just be yours and not assigned to the bank if they have accepted the waiver.
Just an opinion.