I still have my Mom's featherweight that I learned to sew on, made in the 40's. Still purrs along. Went through 2 Singers in my 20's and 30's, got a Brother with some Fancy stitches about then and traded up to a Bernina when I made 75 square dance dresses and got paid $75 apiece! Traded up to another Bernina when a friend was trading up and I gave her $100 for hers, as that was the difference the dealer would giver between hers and mine. Then I found a Viking embroidery machine that I fell in love with! I was still working, figured this would be my retirement machine so I took the plunge. It was D1 and took floppy discs. When I retired and tried to embroider, I found I would need a different set up for my brand new computer that DIDN'T use floppies! So I traded up to the SE and about 4 weeks later the Diamond came out. I stomped my feet and got the dealer to give me the DIamond for what I had paid for the SE, as he knew it was coming out! That said, I am now 71, not in need of a new machine, the Diamond is about 8 years old, the new Diamond Deluxe is lovely but nothing on it would entice me to upgrade at this point.
To your question should you get 10 or 15 years from a machine, yes, treat it right and service it, and you can get many more years than that. Will you? Depends how much you desire the newest bell or whistle that comes out, a larger harp, a special feature that wasn't even invented when we bought that one (embroidery machines were very new when I got my first one). I have 2 sergers, the D1, the featherweight, the Diamond and a couple of antiques, including a treadle. If you are a 1 machine girl that isn't as impusive, I think you will be fine.
My question to you, why would you not want to trade if the occasion should arise that something new pulls at your heart strings? I didn't ever intend to have so many machines, or even change that often, but life happens. I love my hobby/obsession, and I don't do alot of traveling, entertaining, major spending. My car is a 2001 and only has 54,000 miles, still runs good, not looking to trade. But....who knows, I might see a flashy new shiny one that catches my eye, and ..... good luck!