Hello Kristiina Overton,
Thank you for your question. These words are synonyms meaning the same thing. "Yleisesti" word has a little bit more official kind of status at it is connected often with some verb with some suffix. "Yleisesti katsottuna... (generally viewed)", for example.
Let us know if you have any question.
Cheers,
Aarni
Team FinnishPod101.com
What is the difference between yleensa and yleisesti?