Slow Updates

I have a project that produces a roll report. To do this, I have two tables:

T1 (roughly 20,000 records)
ID (Primary Key), PrevAmt, CurrAmt, Action

T2 (roughly 40,000 records)
ID, Amt (linked Excel spreadsheet)

I then run 4 queries in sequence

Q1: Update T1 set PrevAmt=CurrAmt, CurrAmt=0;
Q2: INSERT INTO T1 (ID, PrevAmt, CurrAmt) SELECT ID, 0, 0 FROM T2; /* keys that already exists will fail to insert)*/
Q3: Update T1 INNER JOIN T2 ON T1.ID = T2.ID SET T1.CurrAmt=T1.CurrAmt + T2.Amt;
Q4: Update T1 SET Action = iif(PrevAmt=0 and CurrAmt<>0,"NEW",iif(PrevAmt<>0 and CurrAmt=0,"DROPPED",iif(PrevAmt<>CurrAmt,"CHANGED","UNCHANGED")));

T1 and the queries is in an Access file on a network drive. T2 is a link to an Excel sheet on a network drive.

When I run the queries from a PC on the local LAN, it takes about 2 minutes to update. I consider that acceptible. But I now have to run it from a PC attached to the network via a VPN over a somewhat slow DSL line. The queries take over 20 minutes to run. I want to cut that time down. But the Access file and the Excel file need to stay put as other users use them for other purposes. (Though they know not to access them till after they see my roll report in their in-box.)

What can I do to decrease the update time on this?

Thanks,
David