I would care. 10-15 year old is probably no longer an issue but technically they're a liability and if they were much younger (which at some point they were) they would be a much larger liability as well as an issue if you ever went to work for a competitor and this came to light (like it just did...). It's not to your advantage to have copies of your former employer's IP and possibly even data laying around. Hostile audits are a thing too, again, on 10 to 15 year old code probably not because that code either has changed considerably or it may have been abandoned.