150mcg desogestrel is the same as in Marvelon which is a combined pill containing 30mcg of ethinylestradiol.
So if you use one of the conversion charts online and compare your dose of gel to ethinylestradiol, if it is the same or less potent than 30mcg ethinylestradiol this is fine.
Desogestrel 150mcg has also been studied in combination with 1mg and 1.5mg of oral estradiol as HRT. Endometrial protection was confirmed at these doses.
Desogestrel 150mcg is considered roughly equivalent to 10mg of medroxyprogesterone acetate. These have been compared head to head in other studies including amenorrheic premenopausal women.
