How likely is this transit at Frankfurt?

At least, on the 16th of July, LHA 457 from LAX arrives at the Z concourse and LHA 1458 to Ljubljana leaves from the A concourse.

Z concourse is directly on top of A concourse. You go to the 'V' at the root of Z, where you will go through immigration (pass port check) as you enter the Schengen zone. Then you will go downstairs to the "landside" A concourse to your gate.

You don't have to change concourses or go through any security. Baring an unusual situation at immigration, the whole process should take less than an hour. I've arrived at FRA and been in the Fernbahnhof waiting for a train in less than an hour.

Of course, the whole operation depends on your flight from LA being on time. A late arrival will cut into your transit time.

It looks like if you make the connecting flight, you will get into Ljublyana around 13:40. If you have to take the next flight to Ljubljana, you still get there that day. It's at least a 5 hour train connection from Venice to Ljubljana the next day.

Few notes-
there are hotels right inside the Frankfurt airport if you do end up with a ten-hour layover.

We used Go-Opti shuttle service from Venice to Ljubljana and it took about two hours. They were prompt, courteous, and very professional.

Safe travels!

Thanks Pat and Lee. That helps a lot!