Hopefully, you will get a better answer than this since I'm not an IT guy by any stretch of the imagination. All that I've ever read suggests you should not attempt to use Access over a WAN (VPN). What I can say that has worked for me as a user is having the db split (for all the usual good reasons) but both parts are on a network server. Then each user logs into their own FE (front end) via a terminal service (in my case, it was Citrix) since this doesn't involve the transfer of data across the WAN, but only keyboard and mouse inputs.
An alternative seems to be a SQL type of back end where Access provides the FE tool, but I believe this still can involve large movements of data over the WAN. In absence of a better answer, try Googling something like ms access shared database vpn
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.