U = 7, G = 1, A = 9, I = 5. 

To confirm, 7 + (16)*(94) = 1511.

As I mentioned in my earlier comment, the problem is that just knowing that I = 5 doesn't tell us what the other values are, unless we assume that none of the letters is 0, because there are other solutions, for example:

0 + (26)*(97) = 2522

0 + (67)*(98) = 6566

and perhaps more of a stretch

4 + (08)*(62) = 0500

2 + (06)*(83) = 0500