Travel DB

It's more than just portraits though, the TravelDB also holds information about foreign sims and the relationships of your currently active homeworld sims to them. If deleted, there will no longer be any such relationships.

This mostly stores pics and info of those sims all your sims that ever traveled know from different worlds, like China, Egypt, France, Sims University, Oasis Landing or, if you use NRaas Traveler, any other world your sims traveled to, and vice versa. I guess you know best whether your sims need any of that information. I think the worst that can happen is that all the portraits of "foreign" sims (those with the darker background on the right of your portrait panel) will be gone.

In the end, just keep a backup copy and see what happens. At least deleting it shouldn't break your game.