I, too, have this machine and it is a workhorse as others have said. Maybe it's due for a cleaning?

If you are into vintage, I do all my free motion on a Singer 15-91 built in 1949. It is a straight stitch machine with about 9 inch harp and uses any thread I throw at it (except Isacord) and never seems to have a tension problem... But I know vintage is not for everyone, just a thought!

I understand the frustration of a machine that doesn't want to stitch correctly. But at the cost of machines today, I would certainly take it in for at the least a good cleaning and checkup by certified repairperson. So many issues can be very simple and cheap to fix, that you may decide to keep your current machine.

The Janome 6600 or the new 8900. I have both models.....love them for FMQ. You said you changed needles? You didn't say what size needle.....for Fmq you need a 90/14 topstitch....let us know If that helps. Also check your thread and thread path to see if there are any hang ups or burrs.

I quilt on either a Juki or Babylock Jame. My Daughter uses the same Brother you have. All of them are great at FMQ and straight line quilting. If My seams are real thick I just make a circle around the intersection.

Both my machine are Viking..I love them..I learn the hard way..sometimes it isn't the machine..but the person running it..doing just some little thing wrong..question to ask ur self..did it always do this..if answer is no..then as said it may need a over haul by someone school in it..must cheaper than a machine..if after u do that..it still has trouble.and u are sure it isn't u..then look into a new one..it really does take a lot to wear out most machine..if u need an excuse to ease ur mind for a new one..lol.go for it..

I have this same machine & it is actually very good at all those things. Your machine might need servicing but the most common reasons for it to misbehave is dull or bent needle, needle not in properly, something not right with the threading.
I have found it does best with a Stretch Needle (it has a longer scarf), make sure the needle is placed in the right direction and when threading thread through all 3 holes & have that extension wand at 1 st all the way up & loop directly over the thread spool.
When ever mine starts skipping I change the needle & check threading, it returns to doing well.

I had trouble with my 1500. I did have it serviced by a Brother dealer, and it came back worse. The tech knew nothing about the 4 feed dog positions and had the cam set so you couldn't use the pin feed. I had the manual and got help to fix it. (I can't undo tight screws) Got it fixed and it took an immediate dislike to good thread - Superior for one. I have no idea as to whether the tech futzed with the thread feeding system or not.

I finally had it and traded for a Juki. We'll see how it does.

I'm not brand loyal, I just want something that works. I normally won't touch Brother machines as they support Disney on the embroidery machines. I hate ESPN (Disney owns it)

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Have you had this machine serviced lately? I have the Juki TL98Q which is very much like your Brother 1500 & it is a workhorse and FMQ's beautifully. Have you cleaned the tension disc's, may have lint or a tiny piece of thread behind the disc's, this will cause thread breaking, skipping, etc. If your needle is the wrong size for the material that might cause the issue with going over thick seams. I mended jeans recently that were ripped alongside the back pocket. The Juki darned over the pocket seam, the denim patch, & the jean material with nary a hitch. Was going through probably 8 layers of denim and never broke a thread. Yours should do the same. I know it is very frustrating to mess with a machine when it is not working properly but this sounds like a mechanical issue, could be the timing is off, too. But if you just want another machine,( been there, done that), still wouldn't get rid of my Juki, like it much better than my Bernina, & is equal to my Janome 6600P, just doesn't have all the features. Good luck!!
:)

I have one of the older Singer Black Model 15-91 which I use for FMQ and it is wonderful. I simply would not be without it. It is a very heavy duty machine and will sew thru most anything.