Agreed with others, but I also think if you are willing to invest a ton of time researching, coming up with your short list on such old gear such as the R115, that appears to be of the 1990 vintage so only 25 years old and is solid state, so based on published specs, if you can get one at a good price and the unit is in top condition such that it does not need refurbishing such as a thorough clean up, replacing relays, and recapping then it is worth acquiring.
One thing you can do too is to check with your local repair shop and ask for an estimate for a general clean up, and recapping costs, assuming no other critical parts such as the output devices need to be replace. It won't give you a complete picture but at least for budgeting purposes it should help you make an more informed decsion.
Also, the R115 is a receiver, if you don't need FM/AM, and like Luxman's, then why not look on the power amp, or integrated amp side.