If you find the db running slow on your local computer, it isn't gonna get any faster when opened remotely and in fact will run slower even over ethernet.
Filemaker's design causes a bit of slowness since it transfers the bulk of data to the user and then back. There are databases that react faster but they are not as easy to use.
The first thing to do is to create layouts and scripts specifically for IOS and rethink your approach and design. For instance, use an item layout instead of a portal on a layout with lots of actions on it. Use quickfind to locate the item and then work with it on that layout. Save and find the next item. When done, THEN show the invoice layout and portal and totals. You've minimized the data being transmitted.
Minimize your layouts, you don't have to have 3245 objects on the layout with 22 tabs, 44 portals and 345 calculated fields that need to update just because you sneezed... :)
Study Apple's App Store...