Dosing question

I’m thrilled to be prescribed 15mg of compounded tirzepatide after being on were 2.4 for a year and plateaued. I realize this is a huge jump, so I plan to take half doses (7.5mg) to stretch it out to start. (I’ve taken 7.5 tirz historically and have been fine).

Is there a way I can calculate this or should I just eyeball it?