I've never heard of warranty insurance on a 15 year old car. Learn something every day.
Oh yeah, you want to pay for it, someone will be there to sell it to you. Crazy, but it happens.
Most of the purchased extra warranties (which are a horribly overpriced undercovered item to begin with) just cover the major mechanicals of the engine, and do not cover any engine management components.
Good news is, often times once you find out the mistake you made in purchasing it in the first place, and realize how useless they usually are, if it has not actually been used you can get a refund for at least a substantial percentage of the cost (maybe 80%), and put that towards the actual repair that is necessary.
However, since a lot of people actually FINANCE this stuff, you won't actually get a "chunk of cash" back. And you end up paying a lot more for them. Gotta read the fine print.
My sister got caught in a scam like this, when she bought her '96 Jetta GLX, which already had a CPO warranty from Volkswagen as it was only 18 months old at the time. They got her for a whopping $2800! And the only thing it really "covered" was if a rod blew out the side of the block. Fortunately, I knew the sales manager at the dealership, and got it refunded 100% only two days later for her. Turns out she drove that car another decade and 150k miles and never did spend collectively for everything that needed to be repaired on that car in that time anywhere near $2800.