I need a self-store hose to stretch over 15 metres. Which one do I get?

Brotec self-store hose is manufactured in 3 lengths. They are 7.5 metres, 15 metres and 30 metres. These lengths relate to the linear amount of tubing in the coil. To ascertain the working length you need to divide the linear length by 2. Brotec recommend that you only stretch the coil out to 50% of its linear length. Therefore a 7.5 metre coil will have a working length of 3-4 metres, a 15 metre coil will have a working length of 7.5 metres and a 30 metre coil will have a working length of 15 metres. If the coils are continually extended beyond their specified working length they lose their ability to retract.