Not sure where you buy from but good quality plastic windows have definitely more than 15 years durability. Ie ours are 20 and no sign of weakening isolation.
We have cca proper winters (maybe not this year) and thermal+humidity sensors in most rooms so a badly insulating window/door would be noticed quickly.
We have cca proper winters (maybe not this year) and thermal+humidity sensors in most rooms so a badly insulating window/door would be noticed quickly.