keep the 15-91 ! It is a workhorse and if you ever sew anything heavier, you will be glad you have it. easy to maintain & practically nothing goes wrong. other vintage Singers that are great are 301 (aluminum)401,and the wonderful 201. my Bernina is my 2nd machine since I started with the 201. it purrs and is so soothing to sew with. with piecing, you really don't need a zigzag machine. there is a vintage Singer Yahoo group that is always ready to help too.