I went PA 28 - TB10 - AC11, over the space of two years did about I hour each time to convert to each stage of complexity. 15 hours is a rip off.
But do read the manuals for the vp prop settings also recomend John Deakins articles on "www.avweb.com" to understand vp props manifold pressure etc.
Also understand the emergency gear down proceedures for your type. I played with mine whilst it was on jacks for star annual, and learnt a lot.