I bought my condo about 8 years ago when 35 year mortgages were available in Canada and I locked in that rate. After 5 years, I refinanced it (or whatever it is you do), and locked in a lower rate. Kept my payment the same and knocked literally an extra 5 years off the mortgage. So after 8 years I now have 22 years left on my originally 35 year mortgage.
In a couple of years when I go to renegotiate it, I doubt I'll get as good a deal, but I should be in good standing regardless.
And while I am a mathie, compounding interest rates just never make much sense to me without sitting down and working it all out. But even at a glance I know 3.4% is a hell of a lot less than 7% and it's a rate I wouldn't budge from unless you were forcing me (possibly literally, with a bulldozer...)