Is there a way to increase the user logged in timeout?

Alas, no. It's 20 mins in the Commerce API context. What you can do is set up a client-side detector to listen to page events and pop up a warning if the user idles. But you can't stop them from being prompted to log back in when they do an action which hits the server if they haven't hit the server in 20 mins. That can be heavy on the client, though, since it's a single page application and not every click hits the server.

It's a PCI requirement and I believe the limit was lowered to 15 minutes.