The way I read the statement from Treasury, is that an additional 15% is applied to funds in excess of $3M. So first they calculate 15% tax on earnings in an accumulation account. Then, if you are only in accumulation mode, they calculate the earnings on funds in excess of $3M and apply an additional 15% tax to these earnings. If you have both pension and accumulation accounts, they will apply the usual 15% tax on funds in the accumulation account, and they they will total the pension and accumulation accounts and apply an additional 15% to the proportion of earnings on any totalled amounts greater than $3M. I stand to be corrected.
