How does an E6 have 6 service stripes?

not an issue, as an E6 at 15 years all it takes is missing the cut-off by a few points once or twice

Technically it is possible considering 20 years is cap for E-6

i had 8 when i retired in 09 and no art 15s

I retired at 20 years as an E6. Nothing to be ashamed of. I just happened to be in a job that was top heavy for many years.

Somewhere someone missed the boat but he could have had a bad run . My goal was to see as many people make E-7 or better. But if they don't help themselves you can't do it for them . All branches of military have courses that must be completed to advance in grade and rank and require those wanting to be promoted to achieve . The old saying God helps those that help themselves and along with rank comes responsibility and most important you have to be in the slot or billet .

First off, congratulations on your recent promotion. When you see this always assume first that this SSG may be in a particular MOS that doesn't have many openings for E7. Always give people the chance to prove their character before assuming anything.

Could possibly be prior service or just NJP’d and cleaned up and re-enlisted. You can complete 20 years of active service as an E-6 after all.

I did 20 retired as an E6 I was in a small MOS and getting E5 and E6 was really hard both times I was promoted with well over 900 points. I was an 11B for three years I could have climbed the ladder really quick but I went to school as an E4 picked up 84B as an MOS there was only 250 photographers in the Army.

Reserve or national guard time is possible

Unfortunately, it happens. Many, many variables to include MOS, funding, drawn down, etc. This is much more common in the Air Force. Don't assume based upon rank. Some of the best don't get the promotions and, unfortunately, some who are promoted shouldn't be. This holds true for both enlisted and officer but never WO's :-).