If they have adjustable-rate mortgages, yes. But in a sense, this will be tempered by the savings they are realizing today.
> Or has everyone refinanced for fixed interest mortgages.
Some have. I'm not sure of the breakdown.
So but ... are you looking for doom-and-gloom of interest rates going up? I had an adjustable mortgage for much of the 90s, and largely saw my payment go up over the years. But: it started out low enough that the total interest I paid from, say, 1994-1999 was less than I would have paid if I had gotten a fixed mortgage, even though there were some times (1996 sticks in my mind as a local maximum?) where my payment was more than a fixed would have been.
It's tricky. The right thing to do has more to do with where you think your cash flow situation is headed. YMMV, and I'm not being paid enough to call this 'advice' -- seek a professional before doing anything.