Some of the Differences between the 12000 and 15000:
15000 is a little larger in size, enough that if your sewing table has an insert it may not be large enough for a 15000
Screen on the 15K is superior: in size, clarity and color. The screen on the 12K wasted a lot of space with that "dial" on the bottom
SAME hoops. except the AQS22 comes with the 15k, it's not an extra. Both machines the RE18 hoops are extra purchases.
Embroidery Stitch Limit: 100,000 stitches vs. 200,000 stitches
Clothsetter: Uses the same one for both
Decorative Stitches: More available on the 15k,
Tapered Stitches: Only on the 15k
HP foot and Plate: Only on the 15k
Ruler Work foot comes with 15k
WiFi Connectivity: Only on the 15k
IPad Apps: Free: AcuEdit, AcuSetter, AcuSketch, AcuMonitor: available to use on the 15000 very easily with WiFi connection
AcuDesign: Free with purchase of 15000 with the code provided.
The AcuDesign and AcuSketch apps can be used with a 12000 but the designs have to be saved to a storage source and then loaded onto the 12000
I'm sure there are more differences, but All in all they are both fabulous machines, I have both, and use them both!