Dual Major - Upper Level Credit Requirements for 2nd Degree

[StudiousTraveller]

I already have a Bachelor of Science but am now looking at a Bachelor of Arts with TESU. I originally thought I'd do the BA in Psychology but after learning more about dual majors I'd like to consider a BA in Psychology and History. 

I understand I need to do UL credits (18 I believe?) but have a question about that-

Would I need to do 18 UL credits in each AOS or just 18 UL credits spread out across Psychology and History classes? 

For example I seem to be able to find more UL Psych classes (that interest me) so can I do 15 UL in Psych and 3 UL in History to satisfy the UL credit requirments?

Thank you!