After thinking about it little more I have decided to delete one character. I thought, If I delete it now, buy foundry slots, and than create new character in place of the one I'm going to delete, I can still level him up to level 5 and get the free Odyssey for him.
Well... unfortunately it didn't work. Not only I still can't buy foundry slots, I also can't create any new characters to replace the one I just deleted!
Son now I'm without foundry and I have ended life of one little green alien for nothing!
I'm currently silver player, maybe I should feel lucky that I can still keep those 3 characters instead of just 2 like the new silver players, but I thought that If I had 4 character slots in the past I'm not going to ever loose them.