My mom has the Janome 15000, and it's a great machine. She just got it in July, but has done quite a bit of embroidery on it, and is starting to FMQ. I've used it for quilting as well, and it's pretty great. I think she paid just under $7000 Cdn for it, with the trade-in of her 20-yr-old embroidery machine.
If you don't do much large embroidery, I would consider getting a smaller embroidery machine and a separate sewing machine with a longer bed for piecing and quilting. The reason the top-of-the-line sewing/embroidery machines are so expensive is that they can use really big hoops for giant embroider, and if you mostly do monogramming, that isn't necessary. Having a separate machine for quilting allows you to embroider and sew at the same time if you want (efficient!), and you could get two separate machines for $4-5000 combined.
I was considering a big embroidery machine like the Janome 15000 myself, but ended up getting a basic Viking Sapphire instead, and I'm glad I did. I wanted the big machine for the large quilting area, and I got that at a much more affordable price. When I get an embroidery machine, it will be a separate unit. If I was to buy right now, I would probably get the Janome MemoryCraft 500E, although I haven't used it to see if I like it, and haven't done much comparison shopping.
You should think about how much room you have, whether you want to sew and embroider at the same time, and how large a hoop you need for embroidery before deciding. My mom made the right choice getting the 15000 because she has limited space, and doesn't have the strength to be moving heavy machines around to switch from embroidery to sewing. Because of my space, age, budget and usage, separate is better for me.
I hope this helps. Good luck with your purchase, and please tell us what you decide!