If TM's passing percentage increases by 10-15 percent that would mean he would be a 67 to 72 percent passer.
It depends on how you calculate it. For example, a 10% increase from 57% is 5.7%. That would put him in the lower 60's. I think that # may be attainable if everyone around him plays just a bit better (which is reasonable given the improvements in the receiving corp and # of returning starters). One other factor that will impact his %, is oddly enough, the defense. If Taylor his playing with a lead, his stats will improve. If we are consistently playing catch-up, that won't play to his strengths.
Put me squarely in the camp that Taylor will put up better #'s this year (hey, it's spring - why not be optimistic). There are a number of factors already listed in this thread that will provide some tailwind for him - and I hope for great things this year.