Is arteriosclerosis reversible?

Not really: Don't believe everything you hear. Atherosclerosis can be stabilized with current meds/treatments but significant regression (>10%) is extremely difficult to demonstrate in humans. Atherosclerosis is a chronic disease. There is no "cure".

Possible: There are several large cardiac trials of statins that suggest that aggressive lowering of lipids may cause some regression but the long term data on this is still missing. Stabilizing the process may ultimately prove to be as important as regression.