How big is the payment shock risk facing the subprime market as interest-only mortgages begin to re-set and borrowers see their payments rise? The answer will depend in large part on how the economy fares in the months ahead. For the most part, subprime interest-only loans have performed surprisingly well, relative to other types of hybrid ARMs in recent years. But don’t let that solid performance fool you: analysts at Fitch Ratings are making