15 to 20 specs of dust/hair?
unless they are fairly large they are do not have any significant impact on the quality of your lens. Since it is a zoom lens you will always have noticable dust on the internal elements of your lens. The cost to send your lens to service, have it cleaned, will be relatively high - and then when you get it back it will have dust in different places - and gain more in time.
But - if they are large specs then you may consider getting it cleaned.
Seriously though - some dust inside the lens is no problem at all.
hair - hmm - that sounds a little weird...
|No Lifeguard on Duty by io_bg|
from Break the rules
|Inside A Clock Tower by poppyjk|
from Gear or Gears
|READY FOR A MISSION by DIM POL|
from Fighter aircraft