The barrel length on both of them are the same, so other then capacity the main differences is the frame size. The 15+1 is a little bigger in height and width. If you wanted to compare the two in more depth on the size and other factors I would advise going to Bersa's website where they have all the specific info on them.
Link to website - https://bersa.eagleimportsinc.com/bersa/firearms/

not the same gun this one is a single stack frame and the 15+1 is a wider double stack frame

Jim, yes Sir it is a "Single Stack", 8+1, slimmer version of the "Double Stack" 15+1 Bersa Thunder.