Thanks for the responses.
Frankies Girl--I remembered that you recently dealt with these issues, so I knew you would have the answer!
Saverocity--yes, as I said, the $1500 would not get me to the Admiral level. Hence, my inquiry as to whether I could just toss the $1500 in with the other inherited IRA since it is already at the Admiral level. But, alas, it looks like that is not an option.
I think what I will do it open a separate Traditional IRA with Vanguard and invest in VTSMX.
Wait a sec--hold the phone. I already maxed out ($6500--yeah, I'm old) my 2013 Roth IRA. So I can't put any $$ into a Traditional IRA for 2013, can I? Shucks.