This is a super cocktail. We started by doubling the quantities here and then adjusted. With 60 ml gin / 15 ml lime / 22.5 St Germain. This proved a tad sharp. However, 60 ml gin / 15 ml lime / 30 ml St Germain proved to be the perfect balance.
Edit: Actually I see he balance I have suggested here exists in another entry on this site as a French Gimlet …here https://www.diffordsguide.com/cocktails/recipe/10679/french-gimlet?srsltid=AfmBOoqnCD978vqwUW-isJ3kHW2F9y1mma6MjfMgJBbmnNF9AYggXCcg