Does the length of the Cable matter?

The 15’ of cable would definitely be a mistake if your turnable is 16’ feet away from the phono stage.  Otherwise, you should be fine.

At 15 feet you may be entering balanced connection territory to eliminate hum and provide a stronger signal. Just my thought. I’d be most worried about hum. 

IF hum is a problem, adapters exist to convert from rca to Balanced, simply to use a better noise resistant balanced cable for the run.

convert TT preamp out RCA to Balanced, then at the amp convert back from balanced to RCA.

female and male versions exist

various options

As a general rule, as I have been told by repeated 'experts', keep the interconnects as short as possible, ~1 meter.  Amp to speakers can be much longer, but use high quality speaker cable, not lamp cord....

elliottbnewcombjr

IF hum is a problem, adapters exist to convert from rca to Balanced, simply to use a better noise resistant balanced cable for the run.

Using an RCA to XLR adapter does not convert the signal to balanced; the signal will remain unbalanced. As for a noise resistant cable, that’s actually more likely to be an RCA cable. Balanced interconnects usually start with an assumption that they’ll be used in a true balanced circuit, where they’ll benefit from common mode noise rejection.

A phono cartridge is technically a balanced (floating) source. It only becomes unbalanced when you use it with a single ended preamp.