I have a Cape Cod style house that was built in 1945 with an attic as a living space. The trusses are 2x6, 16" apart, and don't span more than 15' across. Do I need to reinforce these trusses or should they continue to hold up? If so, how should I reinforce them?
Unless you are putting unusual loads up there (king size waterbed, full kitchen, concrete sculptures), normal bedroom/living room furniture and a couple of people should still be fine.
Ceiling cracks in the lower level will be the first indication of undue stress.
Span tables at: http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
Suggest 8-11 ft max span for a 2x6, depending on species.
So this is unsafe.
The reverse calculator suggests a 2x10 would do it.
I'd suggest getting an engineer in to look at it.