Using a VPN with a Jet/ACE BE can be painfully slow and you can't fix it. Remote desktop (via VPN) is fine as is Citrix but having the Access FE on your local computer and using the VPN to link to the BE is not a good solution.
If you can't implement Remote Desktop or Citrix, then the best solution is to convert the Jet/ACE BE to SQL Server. This will cause other problems if your FE is not designed to be used with a server based BE. For starters, if your forms are bound to queries without WHERE clause or directly to tables, you will be asking SQL Server to download the entire contents of a table each time you open a form. Think about how expensive this is over a LAN let alone over the internet and encumbered by a VPN on top. At best, your internet connection is about 10% the speed of your average LAN so the VPN will always be slow. The only way to improve that is to reduce the number of rows downloaded when the form opens.
To speed up forms, you need to add search boxes where you type in the "ID" you are looking for, You can use combos, but you should probably use local tables to populate the combos which adds another layer of pain. You can also use search forms that let you specify critera, again, you probably want to keep the tables that populate the combos local. You can populate the local tables each time the app opens and you should also add a refresh option to refresh them on the fly.
Applications designed to work with SQL Server et al will work just fine with Jet/ACE so you don't have to use two design patterns. Just design for SQL Server and Jet/ACE will be just fine.
Think about what it would take to populate the table/s that power the combos. Even without converting the BE, that might give you an immediate boost if that data is downloaded just once when the app opens and then refreshed during the day if necessary. That change alone may give you some breathing room. For me, this is actually trivial since all my combos of the straight code value variety exist in a single table. Therefore, in addition to the table/s of simple codes, I would need to download a trimmed down version of the customer table with just the ID and name, and the same with the orders table and the employees and whatever other combos I need to populate in addition to the simple "code" tables like maritalStatus, Gender, Race, OrderType, etc.