Ladder in play stop loss

[Trigger]

Hi
I thought if i had a £5.00 lay bet at 6.00 and wanted to lose -£15.00 if it went wrong all i would have to do is right click at odds of 1.50.
Only £5.00 was put into the stop at 1.50,I was wondering if someone could tell me how i can do the stop loss to lose -£15.00 when it hits 1.50.
i have tried clicking -£15.00 on the ladder profit column but the stop loss works straight away instead of waiting to hit 1.50.
Don't know if there is an easy way of doing this. Thanks