In reply to Dick, Still a Fat B:
How long did you own them before putting them in to storage?
Manufacturers will tell you to bin them, most recommend a max of 5 or 10 years of use and 5 years on a shop shelf PRIOR to use, but inspecting the rope and retiring it appropriately are the key concerns on ropes of less age than this. Bare in mind the manufacturers will err on the side of caution and AFAIK they can't have an obsolescence date longer than 10 years of use on PPI by EU law.
Your ropes of course could have been manufactured over 15 years ago if the shop had had them for 5 years and you stored them for a while.
However I saw some tests (I think by blue titan) on pretty old rope (IIRC around 20 years old) which had never been used and they found it was as strong as new (I'm deliberately not defining strong here as I couldn't easily google the experiment, but IIRC only tensile strength was tested). So there is debate about how long textile gear lasts and in recent years some manufacturers have upped there estimate from a max usable lifespan of 5 years to 10.
I'd start by inspecting the rope for abrasion or contamination by liquid and run it through your hands with a bend of rope between them and look for soft spots. At the end of the day you then have to decide if you trust it or not and what for (ie trad, sport, top roping etc)
Post edited at 12:15