saying they'll fit because the manufacturer says fits 15" rims is an assumption that will leave you making calls to the manufacturer and either removing the brake system or having to order new rims
on most rims the drop down(depression) to allow the tire to be installed is in the front and the tire gets pushed on with rim facing up .
gn rims are not like most 15 rims , on the gn the basket is reversed making the dish look deeper. the drop down is in the rear of the rim and the rim needs to be face down to install tire , this moving back of the drop down makes it more like a 14 when it comes to clearing a brakecaliper
. the gn aluminum is made the same way and clearance for brakes is still an issue
i can tell you that the gn rim will fit with strange 4psion disc brakes if you have long studs and run a 1" spacer , without the spacer youd need a different rim