While you can't do this in a segment, there are logical tests that you can do in calculated metrics.
I'm assuming that you're starting with a table where you have a column for your calculated metric, and that your dimension on the side is some kind of visitor or session ID. So you can see average clicks per person/session.
What you want to output is for those users that have an average of 15 clicks, return the time on site.
Steps:
In your calculated metric builder, start with an IF function. In the logical test box, put the EQUALS function (if you want avg clicks to be exactly 15, other options are greater than/less than functions).
In metric X put your avg click metric. For metric Y you're going to use a static number and put 15 (or whatever value you want to compare it to).
In value if true, put your time on site metric. And for value if false, put 0.
The result of this will be that it is going to compare your avg clicks to the static number of 15. If it matches, it'll return their time on site, and if not it'll put a 0 there. So it won't completely exclude those people, but you can sort by the column and the 0's will always be at the bottom.