I do not know where you are getting that 2-3%, but a majority of established schools hover around 5% true attrition rate (some higher, some lower). For example, CCOM's website says they had 206 seats for the entering 2015 class. The AOA match results show 191/206 remaining = 7.28%. Additionally, many new schools have slightly higher attrition rates due to a variety of reasons, including: newness, lower entrance stats profile, etc. 15% is not the true attrition as one of our 4th years have stated that many students have either taken a LOA or were held back.
True attrition can only be calculated after a school has been around for 6+ years as the maximum number of years allowed to obtain a degree is 6 years (so this would include those held back or taking LOA and are not graduating with their original class). As a 2nd year, I know that our class currently has 155/162. I know personally of 3-4 people that were held back to repeat year 1. I do not know about LOA students as that information is not given to us. Assuming those 3-4 people graduate within the 6 years, then 158/162 = 2.45% attrition in the pre-clinical years.
Edit: whoops, quoting messed up for some reason.