Exact same here. Used to boil longer and now I go for 5 minutes (had too much boil off and would end up with higher gravity and less starter than I wanted)
Uh, MAYBE 5 minutes. Really just a few minutes to sanitize the lid of the pot/pot itself with steam. I like to use just a scosche more water than I want for my starter and this way I don't boil off much/any.
for me it varies, but i've boiled for as little as 1 minute. the idea is to sterilize the wort and that happens in a few seconds at 212*F. the rest, to my mind, is to create steam to sterilize the pot/flask/etc you're boiling in. certainly nothing wrong with boiling for 15 minutes, but i can't think of any reason such a long boil is necessary. am i missing something?
Personally I boil in a small saucepan for 5 - 10 minutes with the lid on the last few minutes. I sanitize my flask, then i put the hot/boiling wort in the flask, and then put the flask in the ice bath with aluminum foil on the top.