I am remodeling my kitchen & patio. There was a sliding glass door and Kitchen window I removed to open the kitchen to the enclosed patio. Currently, there is a
9 1/2 inch beam that is 15 foot long with a 4x4 post at 8 ft 51/2 inches. Does this
beam need to be changed to take out the 4x4 post? What size beam is needed to meet code for that 15 foot opening without a post.

The beam is larger enough for a 15' opening.

This is a structural change and should be approved by the building department in your area. They may require an engineers drawing.

If on a gable end of house there is less weight on header because of rafters not being above.

Chuck

Describe the "beam", is it two 2X10's with a plywood spacer between the 2Xs?