Confused about injection dosing

Could someone explain the dosing differences between testosterone injections and topical cream? My new prescription is for testosterone at 100 mg/mL, with instructions to inject 0.15 mL (15 mg) twice weekly.

I’m currently on 1.25 mg topical testosterone daily, 5 days a week, and the injectable dose seems much higher by comparison, unless I’m missing something. I’ve used the cream for 6 months, but my testosterone levels haven’t increased at all.