Um..let me see...think it was 1 hour from PA28 to Arrow IV....these days under JAR you are really only talking 5 hours conversion time max - so 10-15 is a little steep.
More than 5 hours? I dont think you need it - lets face it - gear and a new lever. Wow. Mind blowing. Not.
Provided you are already a competent PPL there is no reason why you wouldn't master it full within those 5 hours.
Personally my advice, as an instructor, is find another school.