OK, clarify a bit more.
You say you are vectored 15 miles out. Do you mean track miles, or onto a 15 mile final?
Normally I would vector onto an 8 mile final unless otherwise requested or there was traffic in front.
If you mean extra track miles, it might be because we will put you into a radar "circuit", like a large fixed wing circuit. This means you will be taken onto a downwind (at my airfield) 5 miles north of the airfield, which will give you a 4 mile base leg. We will generally turn you onto a closing heading to intercept the final approach track at 30 degrees.
It may be that because you are a lot more manouverable, you feel this is too large, but a jet would want the miles. You can always ask for vectors direct to an 8 mile final, or to self-position for the approach. If, as you say, there's no traffic, I doubt this would be a problem.
Finally, there could always be more traffic that you don't know about. Pilots often forget that we could be working traffic on multiple frequencies (approach/radar/director/UHF/VHF).
Does that make sense?