Yes - If I had a 15" case, I would shop for a 16" or 17" form.

I would just add a 2” piece of fabric around the perimeters of one piece, then use the other side of the strip to sew to the backing. Or you could sew another row each direction making a sixteen patch, then trim the edges evenly to 17.5, then sew them together. Each side will have partial squares on the edges that will look intentional.

I can sense what you're saying is a great idea, I'm just having a hard time picturing it, sorry, I don't have much experience.

I am imagining from what you're saying a 2" strip going all along the 15" panel, folding it 1" over and sewing it to the back panel so half of it is on the front and half of it is on the back. Is that right? It would be sort of joining the panels over and would look like a 1 inch border all around when the insert is inside.

Your other idea of using an extra row of blocks on either side and trimming them to 17.5 would also work, as I could used the trimmed blocks to complete an extra panel which would also be too short.

So now I have a few ideas to try out this week. I am so thankful for your brilliant suggestions. It really is a blessing to be able to call on the communal and experienced mind of quilters. I'm really looking forward to knowing more about everything related to sewing myself. I can hardly sleep knowing the sewing machine I just got is in the other room, gleaming new.

You are in the right place! I think the QB is invaluable for all of our questions! I also like the fact that there is no such thing as a "dumb" question. Folks here are not "snarky". People on here willingly offer their help and ideas.

Welcome to the board. And glad you "jumped in with both feet". I think you'll be just fine. 1/4" seam is good and like others suggested, a small border around the top would be fine. OR:
since you're making an entire pillowcase. Sew extras to the back where you do the fold over for the closing. This is a good tutorial to watch for a 16" pillow. It's how she does the back that will most likely be exactly what you need to finish the cases.

https://www.youtube.com/watch?time_c...&v=4LJnPEvjdDo

I completely agree. I was enthusiastic about learning how to sew before joining the QB but the warmth and sharing here has made me feel not only welcome but even more excited about this new artistic prospect.

I'm going to look at this video now. Thank you so much for sharing!

I'm not sure where you are in Africa, so stores might be an issue with my "advice." If you are having trouble with the piecing, try glue basting with a washable glue stick first. It will help you as you try to get that perfect seam allowance. If you are now laughing crazily at the impossibility of buying an Elmer's washable school glue stick there, you can try a wheat flour and water paste, a thin one, which will wash out when the cases are washed, which I am assuming will happen before they are put on the pillow form. But now I am wmdering about that. I have a friend in the Peace Corps who is in Madagascar, and it is humorous to look on as she explains over and over to her friends here in the US what living in a third world country means in day to day life. Hang in there. The great thing about quilting is the same thing my mom used to say about accounting: if you must make a mistake, make sure you do it consistently.