Q Is this cable suitable for a 12v 10a charge controller with a 15w solar panel?
A Yes, the cable will be absolutely fine for this purpose.
Q Im using a 60w panel set, into a 12v 10a controller, would this be able to handle this, also is there any power 'drop off' over the length of the cable?
A Yes, the cable will be fine for the job you need. As with most cable there is a small drop off over the length of cable - because of this we always recommend using the minimum cable where possible.