By "Wealth-Building" they simply mean that you start building equity faster with the 15-year, since a higher proportion of your monthly payment goes towards principal. The advantage for the lender is that they get the loan paid back twice as fast and therefore also have less risk should interest rates rise. But for the borrower (at present), the rates for a 15-year fixed are only modestly lower then the 30 year, and of course your payments are much higher since you're paying the loan off twice as fast. I like the 15-year because it forces discipline, but I recently opted to ReFi with a 5-year ARM because the rates are cheaper and I plan to make lots of extra payments to whittle down the Principal.
In terms of switching, only refinance if the rate is better. Otherwise keep your current mortgage and just pay it down faster (assuming no prepayment penalty).
