Welcome to Flyertalk, Joodee1214! I find Frankfurt to be one of the least user friendly, most confusing airports I have been to. People are unhelpful and signage is inadequate. Security is often rude and overly humiliating. So prepare for a bad experience and consider yourself fortunate if you don't get it.

That being the case, even if your inbound flight is 90 minutes late, you should still have enough time to make your connection with your proposed schedule.

Note that just because the tickets are different doesn't necessarily mean you cannot check your bags through. If neither airline is a discount carrier, you can probably do that and avoid the need to enter and exit Germany. I would contact your first carrier and ask if they interline to the second.