I have a spreadsheet where we are showing wins, losses, and total points
scored. We also show the same data but for only the last 15 matches. Is
there a way to have a cell only take the last 15 entries even though there
might be 100 entries.

Currently we have the cell such as this: Cell A1 has the wins inputted as
follows: "=5+5+5+5+5+5+5". As each week passes, we enter another value in
a1. I'd like to use cell a2 to calculate the numbers of the last 15 entries
of a1.

Any help is appreciated.