Floor supported by 2x6 needs to be reinforced?

I'm adding a walk in closet to a space above my garage and a bonus room. The floor is constructed of a 16 foot 2x6 spaming 14 feet attached to a load bearing wall with an additional 12 foot 2x6 spaming another 10 feet. Should I double up the 2x6 or naila 2x8 to the existing 2x6. Plus will doubling up the 2x6 add too much weight. Thx for your help.