You will need the 17.5" rims to replace the tube type 15" rims.  The 19.5" rims will not fit.

The original spacers should fit, but they may need to be replaced if the wedges don't clamp correctly.  You can measure the spacing to determine what width spacer is needed, however, the easiest is to install them and check the wedges for fitment.  

The proper fit of the wedges is for them to contact the cast hub when clamped tight all around the wheel.  If the spacers are the wrong size the wedges will either not contact the hub or will not clamp the rim tight enough to keep it from slipping.