As you mentioned two courses to compare but these both are different courses both have there own pros and cons. In view of salary you will get a same pay scale in starting but  if you have talent in your field you can go further and get a success in the field.

Interior design is a branch of design that covers the designing of the interiors of a room or building. It includes the development of a concept, up to the actual execution of the design. Your degree will expand your understanding of the human need, user experience, site context, and culture.

Fashion designers create original clothing, accessories, and footwear. They sketch designs, select fabrics and patterns, and give instructions on how to make the products they design.

Both are totally different fields with different requirements. If you have a good knowledge of that field then you can earn a good amount of money.

Hope it helps you

All the best